feat: emit null on empty text widget input for nullable columns

Text widget now sends null to the backend when the user clears the
field on a nullable column, and "" on a non-nullable column. Adds a
new force_send_empty_string widget param (default false) to override
the null conversion when callers want a literal empty string stored
on a nullable column.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: gugu

frontend/src/app/components/dashboard/db-table-view/db-table-widgets/db-table-widgets.component.ts

@@ -230,9 +230,12 @@ export class DbTableWidgetsComponent implements OnInit {
 // isCurrency, isBtcAddress, isISO8601, isISO31661Alpha2, isISO31661Alpha3, isISO4217,
 // isDataURI, isMagnetURI, isMimeType, isLatLong, isSlug, isStrongPassword, isTaxID, isVAT
 // OR use "regex" with a regex parameter for custom pattern matching
+// force_send_empty_string: when true, always send "" to the backend on clear,
+// even if the column is nullable. Default false (cleared input becomes NULL on nullable columns).
 {
   "validate": null,
-  "regex": null
+  "regex": null,
+  "force_send_empty_string": false
 }`,
 		Textarea: `// provide number of strings to show.
 {

frontend/src/app/components/ui-components/record-edit-fields/text/text.component.html

@@ -8,8 +8,8 @@
         [validateType]="validateType"
         [regexPattern]="regexPattern"
         attr.data-testid="record-{{label()}}-text"
-        [(ngModel)]="value" (ngModelChange)="onFieldChange.emit($event)">
-    @if (maxLength && maxLength > 0 && value() && (maxLength - value().length) < 100) {
+        [(ngModel)]="value" (ngModelChange)="handleValueChange($event)">
+    @if (maxLength && maxLength > 0 && value() && 100 > (maxLength - value().length)) {
         <div matSuffix class="counter">{{value().length}} / {{maxLength}}</div>
     }
     @if (textField.errors?.['required']) {

frontend/src/app/components/ui-components/record-edit-fields/text/text.component.spec.ts

@@ -46,7 +46,9 @@ describe('TextEditComponent', () => {
 	});
 
 	it('should parse regexPattern from widget params', () => {
-		fixture.componentRef.setInput('widgetStructure', { widget_params: { validate: 'regex', regex: '^[a-z]+$' } } as any);
+		fixture.componentRef.setInput('widgetStructure', {
+			widget_params: { validate: 'regex', regex: '^[a-z]+$' },
+		} as any);
 		component.ngOnInit();
 		expect(component.regexPattern).toBe('^[a-z]+$');
 	});
@@ -80,4 +82,49 @@ describe('TextEditComponent', () => {
 		component.validateType = 'customValidator';
 		expect(component.getValidationErrorMessage()).toBe('Invalid customValidator');
 	});
+
+	it('should default forceSendEmptyString to false when widget_params omits the key', () => {
+		fixture.componentRef.setInput('widgetStructure', { widget_params: { validate: null, regex: null } } as any);
+		component.ngOnInit();
+		expect(component.forceSendEmptyString).toBe(false);
+	});
+
+	it('should emit null on empty input when column is nullable and force_send_empty_string is not set', () => {
+		fixture.componentRef.setInput('structure', { allow_null: true } as any);
+		component.ngOnInit();
+		const emitted: any[] = [];
+		component.onFieldChange.subscribe((v) => emitted.push(v));
+		component.handleValueChange('');
+		expect(emitted).toEqual([null]);
+	});
+
+	it('should emit empty string on empty input when column is not nullable', () => {
+		fixture.componentRef.setInput('structure', { allow_null: false } as any);
+		component.ngOnInit();
+		const emitted: any[] = [];
+		component.onFieldChange.subscribe((v) => emitted.push(v));
+		component.handleValueChange('');
+		expect(emitted).toEqual(['']);
+	});
+
+	it('should emit empty string on empty input when force_send_empty_string is true even on nullable column', () => {
+		fixture.componentRef.setInput('structure', { allow_null: true } as any);
+		fixture.componentRef.setInput('widgetStructure', {
+			widget_params: { force_send_empty_string: true },
+		} as any);
+		component.ngOnInit();
+		const emitted: any[] = [];
+		component.onFieldChange.subscribe((v) => emitted.push(v));
+		component.handleValueChange('');
+		expect(emitted).toEqual(['']);
+	});
+
+	it('should emit non-empty value unchanged regardless of nullability', () => {
+		fixture.componentRef.setInput('structure', { allow_null: true } as any);
+		component.ngOnInit();
+		const emitted: any[] = [];
+		component.onFieldChange.subscribe((v) => emitted.push(v));
+		component.handleValueChange('hello');
+		expect(emitted).toEqual(['hello']);
+	});
 });

frontend/src/app/components/ui-components/record-edit-fields/text/text.component.ts

@@ -20,6 +20,7 @@ export class TextEditComponent extends BaseEditFieldComponent implements OnInit
 	maxLength: number | null = null;
 	validateType: string | null = null;
 	regexPattern: string | null = null;
+	forceSendEmptyString: boolean = false;
 
 	override ngOnInit(): void {
 		super.ngOnInit();
@@ -35,9 +36,18 @@ export class TextEditComponent extends BaseEditFieldComponent implements OnInit
 
 			this.validateType = params.validate || null;
 			this.regexPattern = params.regex || null;
+			this.forceSendEmptyString = !!params.force_send_empty_string;
 		}
 	}
 
+	handleValueChange(v: string | null): void {
+		if (v === '' && !this.forceSendEmptyString && this.structure()?.allow_null === true) {
+			this.onFieldChange.emit(null);
+			return;
+		}
+		this.onFieldChange.emit(v);
+	}
+
 	getValidationErrorMessage(): string {
 		if (!this.validateType) {
 			return '';