Document morphMany empty-array serialization

docusaurus/docs/cms/api/document-service/populate.md

@@ -246,6 +246,10 @@ Omit `sort` from a `populate` object to preserve the default connect order (the
 
 ## Components & Dynamic Zones
 
+:::note
+When populated, empty `morphMany` relations (including `type: 'media', multiple: true` fields such as a gallery) return `[]` instead of `null`, consistent with `oneToMany` and `manyToMany`. See the [morphMany serialization breaking change](/cms/migration/v4-to-v5/breaking-changes/morph-many-serialization) for migration guidance.
+:::
+
 Components are populated the same way as relations:
 
 <Endpoint

docusaurus/docs/cms/api/rest/populate-select.md

@@ -322,3 +322,7 @@ For many-to-many and other join-table relations, an explicit `sort` within a `po
 :::tip Performance tip
 In production, always use explicit population instead of wildcards like `populate=*`. Limit population depth to 2-3 levels and consider centralizing population logic in route middlewares. See <ExternalLink to="https://strapi.io/blog/building-high-performance-strapi-applications-common-pitfalls-and-best-practices" text="Building High-Performance Strapi Applications" /> on the Strapi blog.
 :::
+
+:::note
+When populated, empty `morphMany` relations (including `type: 'media', multiple: true` fields such as a gallery) return `[]` instead of `null`, consistent with `oneToMany` and `manyToMany`. See the [morphMany serialization breaking change](/cms/migration/v4-to-v5/breaking-changes/morph-many-serialization) for migration guidance.
+:::

docusaurus/docs/cms/migration/v4-to-v5/breaking-changes.md

@@ -109,3 +109,4 @@ You can click on the description of any breaking change in the following tables
 | [Upload a file at entry creation is no longer possible](/cms/migration/v4-to-v5/breaking-changes/no-upload-at-entry-creation) | Yes | No |
 | [Components and dynamic zones should be populated using the detailed population strategy](/cms/migration/v4-to-v5/breaking-changes/no-shared-population-strategy-components-dynamic-zones) | Yes | No |
 | [Updating repeatable components with the Document Service API is not recommended](/cms/migration/v4-to-v5/breaking-changes/do-not-update-repeatable-components-with-document-service-api) | Yes | No |
+| [Empty `morphMany` relations return `[]` instead of `null` when populated](/cms/migration/v4-to-v5/breaking-changes/morph-many-serialization) | Yes | No |

docusaurus/docs/cms/migration/v4-to-v5/breaking-changes/morph-many-serialization.md

@@ -0,0 +1,107 @@
+---
+title: Empty morphMany relations return [] instead of null when populated
+description: In Strapi 5, populating an empty morphMany relation or multiple media field returns an empty array instead of null.
+sidebar_label: Empty morphMany returns []
+displayed_sidebar: cmsSidebar
+tags:
+ - breaking changes
+ - Content API
+ - media
+ - morphMany
+ - populate
+ - upgrade to Strapi 5
+---
+
+import Intro from '/docs/snippets/breaking-change-page-intro.md'
+import MigrationIntro from '/docs/snippets/breaking-change-page-migration-intro.md'
+
+# Empty morphMany relations return [] instead of null when populated
+
+<Tldr>
+
+In Strapi 5, populating an empty `morphMany` relation -- including `type: 'media', multiple: true` fields such as a gallery -- returns `[]` instead of `null`. Update client code that checks `field === null` to treat `[]` as the empty state.
+
+</Tldr>
+
+In Strapi 5, empty `morphMany` relations and `type: 'media', multiple: true` fields (such as a gallery) now serialize as an empty array when populated, consistent with `oneToMany` and `manyToMany` relations. Previously, these fields returned `null` when no related entries existed.
+
+<Intro />
+
+<BreakingChangeIdCard plugins />
+
+## Breaking change description
+
+<SideBySideContainer>
+
+<SideBySideColumn>
+
+**In Strapi v4**
+
+Populating an empty `morphMany` relation or a multiple media field returned `null`:
+
+```json
+{
+  "gallery": null
+}
+```
+
+</SideBySideColumn>
+
+<SideBySideColumn>
+
+**In Strapi 5**
+
+Populating an empty `morphMany` relation or a multiple media field returns an empty array:
+
+```json
+{
+  "gallery": []
+}
+```
+
+</SideBySideColumn>
+
+</SideBySideContainer>
+
+## Migration
+
+<MigrationIntro />
+
+### Notes
+
+- This change applies to all `morphMany` relation types, including `type: 'media', multiple: true` fields (for example, gallery fields).
+- The change is unconditional and is not controlled by the `api.documents.strictRelations` setting.
+- See [Document Service API: Populating fields](/cms/api/document-service/populate) and [REST API: Population & Field Selection](/cms/api/rest/populate-select#population) for related information on populating relations.
+
+### Manual procedure
+
+Check client code, webhooks, and integrations that consume populated `morphMany` or multiple media fields.
+
+1. Search your codebase for code that branches on `field === null` or treats `null` as "no value" for populated `morphMany` or multiple media fields.
+2. Replace `null` checks with array checks, for example using `!field?.length`.
+
+<SideBySideContainer>
+<SideBySideColumn>
+
+**Before**
+
+```js
+if (entry.gallery === null) {
+  // handle empty gallery
+}
+```
+
+</SideBySideColumn>
+
+<SideBySideColumn>
+
+**After**
+
+```js
+if (!entry.gallery?.length) {
+  // handle empty gallery
+}
+```
+
+</SideBySideColumn>
+</SideBySideContainer>