fix(ui): array field state to return empty array instead of 0 (#11283)

### What?

This PR fixes an issue where empty array fields would return `0` instead
of an empty array `[]` in form state.

The issue was caused by `rows` being initialized as `undefined` within
the array field reducer.

As a result, `rows` did not exist on array field state when initial
state was empty.

This has been updated to initialize as an empty array (`rows: []`) to
ensure consistent behavior when using `getDataByPath`.

Fixes #10712 


---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
  - https://app.asana.com/0/0/1211439284995184

packages/ui/src/forms/fieldSchemasToFormState/addFieldStatePromise.ts

@@ -380,7 +380,7 @@ export const addFieldStatePromise = async (args: AddFieldStatePromiseArgs): Prom
           },
           {
             promises: [],
-            rows: undefined,
+            rows: [],
           },
         )
 

test/fields/collections/Array/GetDataByPathTest.tsx

@@ -0,0 +1,25 @@
+'use client'
+
+import { useForm } from '@payloadcms/ui'
+import React from 'react'
+
+const GetDataByPathTest: React.FC = () => {
+  const { getDataByPath } = useForm()
+
+  // Test the empty array field
+  const emptyArrayResult = getDataByPath('potentiallyEmptyArray')
+
+  // Render the result directly so e2e test can easily read it
+  return (
+    <div id="getDataByPath-test">
+      <span id="empty-array-result">
+        {Array.isArray(emptyArrayResult) ? 'ARRAY' : String(emptyArrayResult)}
+      </span>
+      <span id="empty-array-length">
+        {Array.isArray(emptyArrayResult) ? emptyArrayResult.length : 'NOT_ARRAY'}
+      </span>
+    </div>
+  )
+}
+
+export default GetDataByPathTest

test/fields/collections/Array/e2e.spec.ts

@@ -637,4 +637,14 @@ describe('Array', () => {
       await expect(subArrayContainer2).toHaveCount(1)
     })
   })
+  test('should return empty array from getDataByPath for array fields without rows', async () => {
+    await page.goto(url.create)
+
+    // Wait for the test component to render
+    await page.waitForSelector('#getDataByPath-test')
+
+    // Check that getDataByPath returned an empty array, not 0
+    await expect(page.locator('#empty-array-result')).toHaveText('ARRAY')
+    await expect(page.locator('#empty-array-length')).toHaveText('0')
+  })
 })

test/fields/collections/Array/index.ts

@@ -277,6 +277,15 @@ const ArrayFields: CollectionConfig = {
         },
       ],
     },
+    {
+      name: 'getDataByPathTest',
+      type: 'ui',
+      admin: {
+        components: {
+          Field: '/collections/Array/GetDataByPathTest.js',
+        },
+      },
+    },
   ],
   slug: arrayFieldsSlug,
   versions: true,

test/fields/payload-types.ts

@@ -557,6 +557,54 @@ export interface BlockField {
         blockType: 'readOnlyBlock';
       }[]
     | null;
+  /**
+   * Change the value of this field to change the enabled blocks of the blocksWithDynamicFilterOptions field. If it's empty, all blocks are enabled.
+   */
+  enabledBlocks?: string | null;
+  blocksWithDynamicFilterOptions?:
+    | (
+        | {
+            block1Text?: string | null;
+            id?: string | null;
+            blockName?: string | null;
+            blockType: 'blockOne';
+          }
+        | {
+            block2Text?: string | null;
+            id?: string | null;
+            blockName?: string | null;
+            blockType: 'blockTwo';
+          }
+        | {
+            block3Text?: string | null;
+            id?: string | null;
+            blockName?: string | null;
+            blockType: 'blockThree';
+          }
+      )[]
+    | null;
+  blocksWithFilterOptions?:
+    | (
+        | {
+            block1Text?: string | null;
+            id?: string | null;
+            blockName?: string | null;
+            blockType: 'blockFour';
+          }
+        | {
+            block2Text?: string | null;
+            id?: string | null;
+            blockName?: string | null;
+            blockType: 'blockFive';
+          }
+        | {
+            block3Text?: string | null;
+            id?: string | null;
+            blockName?: string | null;
+            blockType: 'blockSix';
+          }
+      )[]
+    | null;
   updatedAt: string;
   createdAt: string;
 }
@@ -822,7 +870,7 @@ export interface ConditionalLogic {
     root: {
       type: string;
       children: {
-        type: string;
+        type: any;
         version: number;
         [k: string]: unknown;
       }[];
@@ -2263,6 +2311,57 @@ export interface BlockFieldsSelect<T extends boolean = true> {
               blockName?: T;
             };
       };
+  enabledBlocks?: T;
+  blocksWithDynamicFilterOptions?:
+    | T
+    | {
+        blockOne?:
+          | T
+          | {
+              block1Text?: T;
+              id?: T;
+              blockName?: T;
+            };
+        blockTwo?:
+          | T
+          | {
+              block2Text?: T;
+              id?: T;
+              blockName?: T;
+            };
+        blockThree?:
+          | T
+          | {
+              block3Text?: T;
+              id?: T;
+              blockName?: T;
+            };
+      };
+  blocksWithFilterOptions?:
+    | T
+    | {
+        blockFour?:
+          | T
+          | {
+              block1Text?: T;
+              id?: T;
+              blockName?: T;
+            };
+        blockFive?:
+          | T
+          | {
+              block2Text?: T;
+              id?: T;
+              blockName?: T;
+            };
+        blockSix?:
+          | T
+          | {
+              block3Text?: T;
+              id?: T;
+              blockName?: T;
+            };
+      };
   updatedAt?: T;
   createdAt?: T;
 }

test/form-state/int.spec.ts

@@ -730,4 +730,43 @@ describe('Form State', () => {
       computedTitle: incomingStateFromServer.computedTitle, // This field was not modified locally, so should be updated from the server
     })
   })
+
+  it('should set rows to empty array for empty array fields', async () => {
+    const req = await createLocalReq({ user }, payload)
+
+    // Create a document with an empty array
+    const postData = await payload.create({
+      collection: postsSlug,
+      data: {
+        title: 'Test Post',
+        array: [], // Empty array - this should result in rows: [] in form state
+      },
+    })
+
+    const { state } = await buildFormState({
+      mockRSCs: true,
+      id: postData.id,
+      collectionSlug: postsSlug,
+      data: postData,
+      docPermissions: {
+        create: true,
+        delete: true,
+        fields: true,
+        read: true,
+        readVersions: true,
+        update: true,
+      },
+      docPreferences: {
+        fields: {},
+      },
+      documentFormState: undefined,
+      operation: 'update',
+      renderAllFields: false,
+      req,
+      schemaPath: postsSlug,
+    })
+
+    expect(state.array).toBeDefined()
+    expect(state?.array?.rows).toEqual([]) // should be [] not undefined
+  })
 })