PM-4904: Allow project billing account clears

What was broken
Clearing a billing account from an existing project did not persist. The Work UI sent an explicit null billingAccountId, but the Projects API treated that value as omitted, so the old billing account stayed on the project and appeared again after save.

Root cause
UpdateProjectDto inherited CreateProjectDto billingAccountId parsing, which normalizes null and empty string to undefined. The service clear path depended on a derived flag that is not materialized by class-transformer when only billingAccountId is sent.

What was changed
UpdateProjectDto now owns the update-time billingAccountId field, preserving null and empty string as explicit clear requests while still parsing numeric billing account ids. ProjectService now clears when the DTO billingAccountId is null, in addition to the existing internal clear flag.

Any added/updated tests
Added DTO coverage for null, empty string, and numeric billingAccountId updates. Updated the project service clear test to exercise billingAccountId: null directly.

Author: jmgasper

src/api/project/dto/update-project.dto.spec.ts

@@ -0,0 +1,26 @@
+import { plainToInstance } from 'class-transformer';
+import { validate } from 'class-validator';
+import { UpdateProjectDto } from './update-project.dto';
+
+describe('UpdateProjectDto', () => {
+  it.each([null, ''])(
+    'preserves %p billingAccountId as an explicit clear request',
+    async (billingAccountId) => {
+      const dto = plainToInstance(UpdateProjectDto, {
+        billingAccountId,
+      });
+
+      expect(dto.billingAccountId).toBeNull();
+      await expect(validate(dto)).resolves.toHaveLength(0);
+    },
+  );
+
+  it('parses numeric billingAccountId updates', async () => {
+    const dto = plainToInstance(UpdateProjectDto, {
+      billingAccountId: '80001063',
+    });
+
+    expect(dto.billingAccountId).toBe(80001063);
+    await expect(validate(dto)).resolves.toHaveLength(0);
+  });
+});

src/api/project/dto/update-project.dto.ts

@@ -1,8 +1,33 @@
-import { ApiHideProperty } from '@nestjs/swagger';
+import { ApiHideProperty, ApiPropertyOptional } from '@nestjs/swagger';
 import { Transform } from 'class-transformer';
-import { PartialType } from '@nestjs/mapped-types';
+import { IsNumber, IsOptional } from 'class-validator';
+import { OmitType, PartialType } from '@nestjs/mapped-types';
 import { CreateProjectDto } from './create-project.dto';
 
+/**
+ * Parses optional project billing-account update input.
+ *
+ * @param value Raw `billingAccountId` value from request payload.
+ * @returns Parsed integer, `null` when clearing, or `undefined` when omitted.
+ */
+function parseOptionalNullableInteger(value: unknown): number | null | undefined {
+  if (typeof value === 'undefined') {
+    return undefined;
+  }
+
+  if (value === null || value === '') {
+    return null;
+  }
+
+  const parsed = Number(value);
+
+  if (Number.isNaN(parsed)) {
+    return undefined;
+  }
+
+  return Math.trunc(parsed);
+}
+
 /**
  * Resolves whether the patch payload explicitly requests clearing
  * `billingAccountId`.
@@ -17,9 +42,21 @@ function parseClearBillingAccountFlag(value: unknown): boolean {
 /**
  * Request DTO for `PATCH /projects/:projectId`.
  *
- * Reuses `CreateProjectDto` and makes all fields optional via `PartialType`.
+ * Reuses `CreateProjectDto`, makes all fields optional via `PartialType`, and
+ * allows `billingAccountId` to be explicitly cleared with `null` or `''`.
  */
-export class UpdateProjectDto extends PartialType(CreateProjectDto) {
+export class UpdateProjectDto extends PartialType(
+  OmitType(CreateProjectDto, ['billingAccountId'] as const),
+) {
+  @ApiPropertyOptional({
+    description: 'Project billing account id. Send null or empty string to clear.',
+    nullable: true,
+  })
+  @IsOptional()
+  @Transform(({ value }) => parseOptionalNullableInteger(value))
+  @IsNumber()
+  billingAccountId?: number | null;
+
   @ApiHideProperty()
   @Transform(({ obj }) => parseClearBillingAccountFlag(obj?.billingAccountId))
   clearBillingAccountId?: boolean;

src/api/project/project.service.spec.ts

@@ -1646,8 +1646,8 @@ describe('ProjectService', () => {
     await service.updateProject(
       '1001',
       {
-        clearBillingAccountId: true,
-      } as any,
+        billingAccountId: null,
+      },
       {
         userId: '100',
         isMachine: false,

src/api/project/project.service.ts

@@ -666,8 +666,10 @@ export class ProjectService {
       throw new ForbiddenException('Insufficient permissions');
     }
 
+    const shouldClearBillingAccountId =
+      dto.clearBillingAccountId === true || dto.billingAccountId === null;
     const requestedBillingAccountId =
-      dto.clearBillingAccountId === true
+      shouldClearBillingAccountId
         ? null
         : typeof dto.billingAccountId === 'number'
           ? String(dto.billingAccountId)
@@ -726,7 +728,7 @@ export class ProjectService {
           cancelReason:
             typeof dto.cancelReason === 'string' ? dto.cancelReason : undefined,
           billingAccountId:
-            dto.clearBillingAccountId === true
+            shouldClearBillingAccountId
               ? null
               : typeof dto.billingAccountId === 'number'
                 ? BigInt(dto.billingAccountId)