fix(core): fix stringify logic for interpolated values

Make sure that null, undefined and NaN interpolated values
are rendered consistently with the current ivy approach:
- null and undefined are rendered as empty strings;
- NaN is rendered as-is.

Author: pkozlowski-opensource

packages/core/src/render3/instructions/property_create.ts

@@ -175,11 +175,9 @@ export function propertyUpdateInput(
 export function ɵɵstringifyInterpolation(
     staticStrings: TemplateStringsArray, ...expressionValues: any[]): string {
   // Build the updated content
-
   let content = staticStrings[0];
   for (let i = 1; i < staticStrings.length; i++) {
-    content += expressionValues[i - 1] + renderStringify(staticStrings[i]);
+    content += renderStringify(expressionValues[i - 1]) + staticStrings[i];
   }
-
   return content;
 }

packages/core/test/acceptance/signal-components/dom_property_interpolation.spec.ts

@@ -57,4 +57,39 @@ describe('Signal component DOM property interpolations', () => {
 
     expect(div.title).toBe('Hello, New Name!');
   });
+
+  it('should render null and undefined as empty strings', () => {
+    @Component({
+      signals: true,
+      template: `<div title="a{{null}}b{{undefined}}c">a{{null}}b{{undefined}}c</div>`,
+      standalone: true,
+    })
+    class App {
+    }
+
+    const fixture = TestBed.createComponent(App);
+    const div = fixture.nativeElement.firstChild;
+    fixture.detectChanges();
+    expect(div.title).toBe('abc');
+    // verify that text bindings and interpolated binding rendering is consistent
+    expect(div.title).toBe(div.textContent);
+  });
+
+  it('should render NaN as-is', () => {
+    @Component({
+      signals: true,
+      template: `<div title="a{{notANumber}}b">a{{notANumber}}b</div>`,
+      standalone: true,
+    })
+    class App {
+      notANumber = NaN;
+    }
+
+    const fixture = TestBed.createComponent(App);
+    const div = fixture.nativeElement.firstChild;
+    fixture.detectChanges();
+    expect(div.title).toBe('aNaNb');
+    // verify that text bindings and interpolated binding rendering is consistent
+    expect(div.title).toBe(div.textContent);
+  });
 });