diff --git a/src/addons/block/timeline/components/timeline/timeline.ts b/src/addons/block/timeline/components/timeline/timeline.ts
index e61a52f5c..6969c63c3 100644
--- a/src/addons/block/timeline/components/timeline/timeline.ts
+++ b/src/addons/block/timeline/components/timeline/timeline.ts
@@ -39,10 +39,10 @@ import { CoreLogger } from '@singletons/logger';
 })
 export class AddonBlockTimelineComponent implements OnInit, ICoreBlockComponent {
 
-    sort = new FormControl();
+    sort = new FormControl(AddonBlockTimelineSort.ByDates);
     sort$!: Observable<AddonBlockTimelineSort>;
     sortOptions!: AddonBlockTimelineOption<AddonBlockTimelineSort>[];
-    filter = new FormControl();
+    filter = new FormControl(AddonBlockTimelineFilter.Next30Days);
     filter$!: Observable<AddonBlockTimelineFilter>;
     statusFilterOptions!: AddonBlockTimelineOption<AddonBlockTimelineFilter>[];
     dateFilterOptions!: AddonBlockTimelineOption<AddonBlockTimelineFilter>[];
diff --git a/src/addons/calendar/pages/edit-event/edit-event.ts b/src/addons/calendar/pages/edit-event/edit-event.ts
index a30321547..653aa35b9 100644
--- a/src/addons/calendar/pages/edit-event/edit-event.ts
+++ b/src/addons/calendar/pages/edit-event/edit-event.ts
@@ -78,9 +78,9 @@ export class AddonCalendarEditEventPage implements OnInit, OnDestroy, CanLeave {
 
     // Form variables.
     form: FormGroup;
-    typeControl: FormControl;
-    groupControl: FormControl;
-    descriptionControl: FormControl;
+    typeControl: FormControl<AddonCalendarEventType | null>;
+    groupControl: FormControl<number | null>;
+    descriptionControl: FormControl<string>;
 
     // Reminders.
     remindersEnabled = false;
@@ -103,9 +103,9 @@ export class AddonCalendarEditEventPage implements OnInit, OnDestroy, CanLeave {
         this.form = new FormGroup({});
 
         // Initialize form variables.
-        this.typeControl = this.fb.control('', Validators.required);
-        this.groupControl = this.fb.control('');
-        this.descriptionControl = this.fb.control('');
+        this.typeControl = this.fb.control(null, Validators.required);
+        this.groupControl = this.fb.control(null);
+        this.descriptionControl = this.fb.control('', { nonNullable: true });
         this.form.addControl('name', this.fb.control('', Validators.required));
         this.form.addControl('eventtype', this.typeControl);
         this.form.addControl('categoryid', this.fb.control(''));
@@ -322,11 +322,11 @@ export class AddonCalendarEditEventPage implements OnInit, OnDestroy, CanLeave {
 
         this.form.controls.name.setValue(event.name);
         this.form.controls.timestart.setValue(CoreTimeUtils.toDatetimeFormat(event.timestart * 1000));
-        this.form.controls.eventtype.setValue(event.eventtype);
+        this.typeControl.setValue(event.eventtype as AddonCalendarEventType);
         this.form.controls.categoryid.setValue(event.categoryid || '');
         this.form.controls.courseid.setValue(courseId || '');
         this.form.controls.groupcourseid.setValue(courseId || '');
-        this.form.controls.groupid.setValue(event.groupid || '');
+        this.groupControl.setValue(event.groupid || null);
         this.form.controls.description.setValue(event.description);
         this.form.controls.location.setValue(event.location);
 
@@ -410,7 +410,7 @@ export class AddonCalendarEditEventPage implements OnInit, OnDestroy, CanLeave {
         try {
             await this.loadGroups(courseId);
 
-            this.groupControl.setValue('');
+            this.groupControl.setValue(null);
         } catch (error) {
             CoreDomUtils.showErrorModalDefault(error, 'Error getting data.');
         }
diff --git a/src/addons/mod/assign/feedback/comments/component/comments.ts b/src/addons/mod/assign/feedback/comments/component/comments.ts
index 6271598e2..c5f268f23 100644
--- a/src/addons/mod/assign/feedback/comments/component/comments.ts
+++ b/src/addons/mod/assign/feedback/comments/component/comments.ts
@@ -34,7 +34,7 @@ import { AddonModAssignFeedbackPluginBaseComponent } from '@addons/mod/assign/cl
 })
 export class AddonModAssignFeedbackCommentsComponent extends AddonModAssignFeedbackPluginBaseComponent implements OnInit {
 
-    control?: FormControl;
+    control?: FormControl<string>;
     component = AddonModAssignProvider.COMPONENT;
     text = '';
     isSent = false;
@@ -76,7 +76,7 @@ export class AddonModAssignFeedbackCommentsComponent extends AddonModAssignFeedb
                     }
                 });
             } else if (this.edit) {
-                this.control = this.fb.control(this.text);
+                this.control = this.fb.control(this.text, { nonNullable: true });
             }
         } finally {
             this.loaded = true;
diff --git a/src/addons/mod/assign/submission/onlinetext/component/onlinetext.ts b/src/addons/mod/assign/submission/onlinetext/component/onlinetext.ts
index ca9afe172..f91d185c9 100644
--- a/src/addons/mod/assign/submission/onlinetext/component/onlinetext.ts
+++ b/src/addons/mod/assign/submission/onlinetext/component/onlinetext.ts
@@ -31,7 +31,7 @@ import { AddonModAssignSubmissionOnlineTextPluginData } from '../services/handle
 })
 export class AddonModAssignSubmissionOnlineTextComponent extends AddonModAssignSubmissionPluginBaseComponent implements OnInit {
 
-    control?: FormControl;
+    control?: FormControl<string>;
     words = 0;
     component = AddonModAssignProvider.COMPONENT;
     text = '';
@@ -94,7 +94,7 @@ export class AddonModAssignSubmissionOnlineTextComponent extends AddonModAssignS
                 });
             } else {
                 // Create and add the control.
-                this.control = this.fb.control(this.text);
+                this.control = this.fb.control(this.text, { nonNullable: true });
             }
 
             // Calculate initial words.
diff --git a/src/addons/mod/forum/components/post/post.ts b/src/addons/mod/forum/components/post/post.ts
index 63f44e1b1..ab834b428 100644
--- a/src/addons/mod/forum/components/post/post.ts
+++ b/src/addons/mod/forum/components/post/post.ts
@@ -83,7 +83,7 @@ export class AddonModForumPostComponent implements OnInit, OnDestroy, OnChanges
 
     @ViewChild('replyFormEl') formElement!: ElementRef;
 
-    messageControl = new FormControl();
+    messageControl = new FormControl<string | null>(null);
 
     uniqueId!: string;
     defaultReplySubject!: string;
diff --git a/src/addons/mod/forum/pages/new-discussion/new-discussion.ts b/src/addons/mod/forum/pages/new-discussion/new-discussion.ts
index 6eb86ce9a..8dc2a1563 100644
--- a/src/addons/mod/forum/pages/new-discussion/new-discussion.ts
+++ b/src/addons/mod/forum/pages/new-discussion/new-discussion.ts
@@ -70,7 +70,7 @@ export class AddonModForumNewDiscussionPage implements OnInit, OnDestroy, CanLea
     @ViewChild(CoreEditorRichTextEditorComponent) messageEditor!: CoreEditorRichTextEditorComponent;
 
     component = AddonModForumProvider.COMPONENT;
-    messageControl = new FormControl();
+    messageControl = new FormControl<string | null>(null);
     groupsLoaded = false;
     showGroups = false;
     hasOffline = false;
diff --git a/src/addons/mod/glossary/pages/edit/edit.ts b/src/addons/mod/glossary/pages/edit/edit.ts
index d5d9a3ed8..5705cf257 100644
--- a/src/addons/mod/glossary/pages/edit/edit.ts
+++ b/src/addons/mod/glossary/pages/edit/edit.ts
@@ -58,7 +58,7 @@ export class AddonModGlossaryEditPage implements OnInit, CanLeave {
     courseId!: number;
     loaded = false;
     glossary?: AddonModGlossaryGlossary;
-    definitionControl = new FormControl();
+    definitionControl = new FormControl<string | null>(null);
     categories: AddonModGlossaryCategory[] = [];
     showAliases = true;
     editorExtraParams: Record<string, unknown> = {};
diff --git a/src/addons/mod/lesson/services/lesson-helper.ts b/src/addons/mod/lesson/services/lesson-helper.ts
index b12f4efc2..2fd998089 100644
--- a/src/addons/mod/lesson/services/lesson-helper.ts
+++ b/src/addons/mod/lesson/services/lesson-helper.ts
@@ -369,7 +369,7 @@ export class AddonModLessonHelperProvider {
             };
 
             // Init the control.
-            essayQuestion.control = this.formBuilder.control('');
+            essayQuestion.control = this.formBuilder.control('', { nonNullable: true });
             questionForm.addControl(essayQuestion.textarea.name, essayQuestion.control);
         }
 
@@ -635,7 +635,7 @@ export type AddonModLessonInputQuestion = AddonModLessonQuestionBasicData & {
 export type AddonModLessonEssayQuestion = AddonModLessonQuestionBasicData & {
     useranswer?: string; // User answer, for reviewing.
     textarea?: AddonModLessonTextareaData; // Data for the textarea.
-    control?: FormControl; // Form control.
+    control?: FormControl<string>; // Form control.
 };
 
 /**
diff --git a/src/addons/mod/wiki/pages/edit/edit.ts b/src/addons/mod/wiki/pages/edit/edit.ts
index e1ab5857d..816bd2ffa 100644
--- a/src/addons/mod/wiki/pages/edit/edit.ts
+++ b/src/addons/mod/wiki/pages/edit/edit.ts
@@ -47,7 +47,7 @@ export class AddonModWikiEditPage implements OnInit, OnDestroy, CanLeave {
     courseId?: number; // Course the wiki belongs to.
     title?: string; // Title to display.
     pageForm: FormGroup; // The form group.
-    contentControl: FormControl; // The FormControl for the page content.
+    contentControl: FormControl<string>; // The FormControl for the page content.
     canEditTitle = false; // Whether title can be edited.
     loaded = false; // Whether the data has been loaded.
     component = AddonModWikiProvider.COMPONENT; // Component to link the files to.
@@ -74,7 +74,7 @@ export class AddonModWikiEditPage implements OnInit, OnDestroy, CanLeave {
     constructor(
         protected formBuilder: FormBuilder,
     ) {
-        this.contentControl = this.formBuilder.control('');
+        this.contentControl = this.formBuilder.control('', { nonNullable: true });
         this.pageForm = this.formBuilder.group({});
     }
 
diff --git a/src/addons/mod/workshop/components/assessment-strategy/assessment-strategy.ts b/src/addons/mod/workshop/components/assessment-strategy/assessment-strategy.ts
index 2c53eea33..95f62fd6d 100644
--- a/src/addons/mod/workshop/components/assessment-strategy/assessment-strategy.ts
+++ b/src/addons/mod/workshop/components/assessment-strategy/assessment-strategy.ts
@@ -73,7 +73,7 @@ export class AddonModWorkshopAssessmentStrategyComponent implements OnInit, OnDe
     assessmentStrategyLoaded = false;
     notSupported = false;
     feedbackText = '';
-    feedbackControl = new FormControl();
+    feedbackControl = new FormControl<string | null>(null);
     overallFeedkback = false;
     overallFeedkbackRequired = false;
     component = ADDON_MOD_WORKSHOP_COMPONENT;
diff --git a/src/addons/qtype/essay/component/essay.ts b/src/addons/qtype/essay/component/essay.ts
index d216b87f4..197389dbd 100644
--- a/src/addons/qtype/essay/component/essay.ts
+++ b/src/addons/qtype/essay/component/essay.ts
@@ -32,7 +32,7 @@ import { CoreFileEntry } from '@services/file-helper';
 })
 export class AddonQtypeEssayComponent extends CoreQuestionBaseComponent<AddonModQuizEssayQuestion> {
 
-    formControl?: FormControl;
+    formControl?: FormControl<string | null>;
     attachments?: CoreFileEntry[];
     uploadFilesSupported = false;
 
@@ -52,7 +52,7 @@ export class AddonQtypeEssayComponent extends CoreQuestionBaseComponent<AddonMod
 
         this.initEssayComponent(this.review);
 
-        this.formControl = this.fb.control(this.question?.textarea?.text);
+        this.formControl = this.fb.control(this.question?.textarea?.text ?? null);
 
         if (this.question?.allowsAttachments && this.uploadFilesSupported && !this.review) {
             this.loadAttachments();
diff --git a/src/addons/userprofilefield/checkbox/component/checkbox.ts b/src/addons/userprofilefield/checkbox/component/checkbox.ts
index 83b4a26fc..be762fc87 100644
--- a/src/addons/userprofilefield/checkbox/component/checkbox.ts
+++ b/src/addons/userprofilefield/checkbox/component/checkbox.ts
@@ -27,20 +27,23 @@ import { CoreUtils } from '@services/utils/utils';
     templateUrl: 'addon-user-profile-field-checkbox.html',
     styleUrls: ['./checkbox.scss'],
 })
-export class AddonUserProfileFieldCheckboxComponent extends CoreUserProfileFieldBaseComponent {
+export class AddonUserProfileFieldCheckboxComponent extends CoreUserProfileFieldBaseComponent<boolean> {
 
     /**
      * Create the Form control.
      *
      * @returns Form control.
      */
-    protected createFormControl(field: AuthEmailSignupProfileField): FormControl {
+    protected createFormControl(field: AuthEmailSignupProfileField): FormControl<boolean> {
         const formData = {
             value: CoreUtils.isTrueOrOne(field.defaultdata),
             disabled: this.disabled,
         };
 
-        return new FormControl(formData, this.required && !field.locked ? Validators.requiredTrue : null);
+        return new FormControl(formData, {
+            validators: this.required && !field.locked ? Validators.requiredTrue : null,
+            nonNullable: true,
+        });
     }
 
 }
diff --git a/src/addons/userprofilefield/datetime/component/datetime.ts b/src/addons/userprofilefield/datetime/component/datetime.ts
index c65fec86f..17e28354a 100644
--- a/src/addons/userprofilefield/datetime/component/datetime.ts
+++ b/src/addons/userprofilefield/datetime/component/datetime.ts
@@ -28,7 +28,7 @@ import { CoreUserProfileFieldBaseComponent } from '@features/user/classes/base-p
     selector: 'addon-user-profile-field-datetime',
     templateUrl: 'addon-user-profile-field-datetime.html',
 })
-export class AddonUserProfileFieldDatetimeComponent extends CoreUserProfileFieldBaseComponent {
+export class AddonUserProfileFieldDatetimeComponent extends CoreUserProfileFieldBaseComponent<string | undefined> {
 
     ionDateTimePresentation = 'date';
     min?: string;
@@ -84,13 +84,16 @@ export class AddonUserProfileFieldDatetimeComponent extends CoreUserProfileField
      *
      * @returns Form control.
      */
-    protected createFormControl(field: AuthEmailSignupProfileField): FormControl {
+    protected createFormControl(field: AuthEmailSignupProfileField): FormControl<string | undefined> {
         const formData = {
             value: field.defaultdata != '0' ? field.defaultdata : undefined,
             disabled: this.disabled,
         };
 
-        return new FormControl(formData, this.required && !field.locked ? Validators.required : null);
+        return new FormControl(formData, {
+            validators: this.required && !field.locked ? Validators.required : null,
+            nonNullable: true,
+        });
     }
 
 }
diff --git a/src/core/components/input-errors/input-errors.ts b/src/core/components/input-errors/input-errors.ts
index b43c55cdd..da973bd0d 100644
--- a/src/core/components/input-errors/input-errors.ts
+++ b/src/core/components/input-errors/input-errors.ts
@@ -40,7 +40,7 @@ import { FormControl } from '@angular/forms';
 })
 export class CoreInputErrorsComponent implements OnInit, OnChanges {
 
-    @Input() control?: FormControl; // Needed to be able to check the validity of the input.
+    @Input() control?: FormControl<unknown>; // Needed to be able to check the validity of the input.
     @Input() errorMessages: Record<string, string> = {}; // Error messages to show. Keys must be the name of the error.
     @Input() errorText = ''; // Set other non automatic errors.
     errorKeys: string[] = [];
diff --git a/src/core/features/editor/components/rich-text-editor/rich-text-editor.ts b/src/core/features/editor/components/rich-text-editor/rich-text-editor.ts
index 48787de7f..1ef6e6429 100644
--- a/src/core/features/editor/components/rich-text-editor/rich-text-editor.ts
+++ b/src/core/features/editor/components/rich-text-editor/rich-text-editor.ts
@@ -66,7 +66,7 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
     // @todo Implement ControlValueAccessor https://angular.io/api/forms/ControlValueAccessor.
 
     @Input() placeholder = ''; // Placeholder to set in textarea.
-    @Input() control?: FormControl; // Form control.
+    @Input() control?: FormControl<string | undefined | null>; // Form control.
     @Input() name = 'core-rich-text-editor'; // Name to set to the textarea.
     @Input() component?: string; // The component to link the files to.
     @Input() componentId?: number; // An ID to use in conjunction with the component.
@@ -75,7 +75,7 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
     @Input() contextInstanceId?: number; // The instance ID related to the context.
     @Input() elementId?: string; // An ID to set to the element.
     @Input() draftExtraParams?: Record<string, unknown>; // Extra params to identify the draft.
-    @Output() contentChanged: EventEmitter<string>;
+    @Output() contentChanged: EventEmitter<string | undefined | null>;
 
     @ViewChild('editor') editor?: ElementRef; // WYSIWYG editor.
     @ViewChild('textarea') textarea?: IonTextarea; // Textarea editor.
@@ -190,8 +190,8 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
         // Setup the editor.
         this.editorElement = this.editor?.nativeElement as HTMLDivElement;
         this.setContent(this.control?.value);
-        this.originalContent = this.control?.value;
-        this.lastDraft = this.control?.value;
+        this.originalContent = this.control?.value ?? undefined;
+        this.lastDraft = this.control?.value ?? '';
 
         // Use paragraph on enter.
         // eslint-disable-next-line deprecation/deprecation
@@ -261,19 +261,19 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
 
             // Apply the new content.
             this.setContent(newValue);
-            this.originalContent = newValue;
+            this.originalContent = newValue ?? undefined;
             this.infoMessage = undefined;
 
             // Save a draft so the original content is saved.
-            this.lastDraft = newValue;
+            this.lastDraft = newValue ?? '';
             CoreEditorOffline.saveDraft(
                 this.contextLevel || '',
                 this.contextInstanceId || 0,
                 this.elementId || '',
                 this.draftExtraParams || {},
                 this.pageInstance,
-                newValue,
-                newValue,
+                this.lastDraft,
+                this.originalContent,
             );
         });
 
@@ -579,7 +579,7 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
      * @param value text
      * @returns If value is null only a white space.
      */
-    protected isNullOrWhiteSpace(value: string | null): boolean {
+    protected isNullOrWhiteSpace(value: string | null | undefined): boolean {
         if (value == null || value === undefined) {
             return true;
         }
@@ -595,7 +595,7 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
      *
      * @param value New content.
      */
-    protected setContent(value: string | null): void {
+    protected setContent(value: string | null | undefined): void {
         if (!this.editorElement || !this.textarea) {
             return;
         }
@@ -974,7 +974,7 @@ export class CoreEditorRichTextEditorComponent implements OnInit, AfterViewInit,
                 return;
             }
 
-            const newText = this.control.value;
+            const newText = this.control.value ?? '';
 
             if (this.lastDraft == newText) {
                 // Text hasn't changed, nothing to save.
diff --git a/src/core/features/login/pages/email-signup/email-signup.ts b/src/core/features/login/pages/email-signup/email-signup.ts
index 43797e233..45cb6f9fc 100644
--- a/src/core/features/login/pages/email-signup/email-signup.ts
+++ b/src/core/features/login/pages/email-signup/email-signup.ts
@@ -69,8 +69,8 @@ export class CoreLoginEmailSignupPage implements OnInit {
 
     // Data for age verification.
     ageVerificationForm: FormGroup;
-    countryControl: FormControl;
-    signUpCountryControl?: FormControl;
+    countryControl: FormControl<string>;
+    signUpCountryControl?: FormControl<string>;
     isMinor = false; // Whether the user is minor age.
     ageDigitalConsentVerification?: boolean; // Whether the age verification is enabled.
     supportName?: string;
@@ -93,7 +93,7 @@ export class CoreLoginEmailSignupPage implements OnInit {
         this.ageVerificationForm = this.fb.group({
             age: ['', Validators.required],
         });
-        this.countryControl = this.fb.control('', Validators.required);
+        this.countryControl = this.fb.control('', { validators: Validators.required, nonNullable: true });
         this.ageVerificationForm.addControl('country', this.countryControl);
 
         // Create the signupForm with the basic controls. More controls will be added later.
@@ -141,7 +141,7 @@ export class CoreLoginEmailSignupPage implements OnInit {
      */
     protected completeFormGroup(): void {
         this.signupForm.addControl('city', this.fb.control(this.settings?.defaultcity || ''));
-        this.signUpCountryControl = this.fb.control(this.settings?.country || '');
+        this.signUpCountryControl = this.fb.control(this.settings?.country || '', { nonNullable: true });
         this.signupForm.addControl('country', this.signUpCountryControl);
 
         // Add the name fields.
diff --git a/src/core/features/user/classes/base-profilefield-component.ts b/src/core/features/user/classes/base-profilefield-component.ts
index 78a7fea8c..9a61cf327 100644
--- a/src/core/features/user/classes/base-profilefield-component.ts
+++ b/src/core/features/user/classes/base-profilefield-component.ts
@@ -24,7 +24,7 @@ import { CoreUserProfileField } from '@features/user/services/user';
 @Component({
     template: '',
 })
-export abstract class CoreUserProfileFieldBaseComponent implements OnInit {
+export abstract class CoreUserProfileFieldBaseComponent<T = string> implements OnInit {
 
     @Input() field?: AuthEmailSignupProfileField | CoreUserProfileField; // The profile field to be rendered.
     @Input() signup = false; // True if editing the field in signup. Defaults to false.
@@ -36,7 +36,7 @@ export abstract class CoreUserProfileFieldBaseComponent implements OnInit {
     @Input() contextInstanceId?: number; // The instance ID related to the context.
     @Input() courseId?: number; // Course ID the field belongs to (if any). It can be used to improve performance with filters.
 
-    control?: FormControl;
+    control?: FormControl<T>;
     modelName = '';
     value?: string;
     required?: boolean;
@@ -91,13 +91,16 @@ export abstract class CoreUserProfileFieldBaseComponent implements OnInit {
      *
      * @returns Form control.
      */
-    protected createFormControl(field: AuthEmailSignupProfileField): FormControl {
+    protected createFormControl(field: AuthEmailSignupProfileField): FormControl<T> {
         const formData = {
-            value: field.defaultdata,
+            value: (field.defaultdata ?? '') as T,
             disabled: this.disabled,
         };
 
-        return new FormControl(formData, this.required && !field.locked ? Validators.required : null);
+        return new FormControl(formData, {
+            validators: this.required && !field.locked ? Validators.required : null,
+            nonNullable: true,
+        });
     }
 
 }
diff --git a/src/core/utils/rxjs.ts b/src/core/utils/rxjs.ts
index 63b959856..df1693191 100644
--- a/src/core/utils/rxjs.ts
+++ b/src/core/utils/rxjs.ts
@@ -22,10 +22,10 @@ import { catchError, filter } from 'rxjs/operators';
  * @param control Form control.
  * @returns Form control value observable.
  */
-export function formControlValue<T = unknown>(control: FormControl): Observable<T> {
+export function formControlValue<T = unknown>(control: FormControl<T | null>): Observable<T> {
     return control.valueChanges.pipe(
         startWithOnSubscribed(() => control.value),
-        filter(value => value !== null),
+        filter((value): value is T => value !== null),
     );
 }