Add comprehensive tests for GitHub API validators and vNull

Co-authored-by: joshspicer <23246594+joshspicer@users.noreply.github.com>

Author: Copilot

src/platform/configuration/test/common/validator.spec.ts

@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { describe, expect, it } from 'vitest';
-import { vBoolean, vNumber, vObj, vRequired, vString } from '../../common/validator';
+import { vBoolean, vNull, vNumber, vObj, vRequired, vString, vUnion } from '../../common/validator';
 
 describe('vRequired', () => {
 	it('should mark a field as required', () => {
@@ -160,3 +160,48 @@ describe('vRequired', () => {
 		expect(result2.error).toBeDefined();
 	});
 });
+
+describe('vNull', () => {
+	it('should validate null values', () => {
+		const validator = vNull();
+
+		const result = validator.validate(null);
+		expect(result.error).toBeUndefined();
+		expect(result.content).toBe(null);
+	});
+
+	it('should reject non-null values', () => {
+		const validator = vNull();
+
+		const result1 = validator.validate(undefined);
+		expect(result1.error).toBeDefined();
+		expect(result1.error?.message).toContain("Expected null");
+
+		const result2 = validator.validate("string");
+		expect(result2.error).toBeDefined();
+
+		const result3 = validator.validate(0);
+		expect(result3.error).toBeDefined();
+	});
+
+	it('should work with vUnion for nullable fields', () => {
+		const validator = vObj({
+			name: vRequired(vUnion(vString(), vNull())),
+			age: vNumber(),
+		});
+
+		// null value should be valid
+		const result1 = validator.validate({ name: null, age: 25 });
+		expect(result1.error).toBeUndefined();
+		expect(result1.content).toEqual({ name: null, age: 25 });
+
+		// string value should also be valid
+		const result2 = validator.validate({ name: "John", age: 25 });
+		expect(result2.error).toBeUndefined();
+		expect(result2.content).toEqual({ name: "John", age: 25 });
+
+		// other types should fail
+		const result3 = validator.validate({ name: 123, age: 25 });
+		expect(result3.error).toBeDefined();
+	});
+});