Add documentation for single permission per DSC_DatabaseObjectPermission instance

Co-authored-by: johlju <[email protected]>

Author: Copilot

CHANGELOG.md

@@ -176,6 +176,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- `SqlDatabaseObjectPermission`
+  - Added documentation clarifying that each `DSC_DatabaseObjectPermission`
+    instance can only contain a single permission name. Specifying multiple
+    permissions as a comma-separated string causes an error
+    ([issue #2020](https://github.com/dsccommunity/SqlServerDsc/issues/2020)).
 - `Get-SqlDscRSSetupConfiguration`
   - Fixed issue where the function doesn't provide an output for SSRS 2016 instances
     because registry paths were using `InstanceName` instead of `InstanceId`.

source/DSCResources/DSC_SqlDatabaseObjectPermission/README.md

@@ -20,4 +20,48 @@ property names of the [ObjectPermissionSet](https://docs.microsoft.com/en-us/dot
 
 ## Known issues
 
+### Only one permission per `DSC_DatabaseObjectPermission` instance
+
+Each `DSC_DatabaseObjectPermission` instance can only contain a single permission
+name. When multiple permissions need to be configured for the same state (e.g.,
+`Grant`), each permission must be specified in a separate `DSC_DatabaseObjectPermission`
+block. Specifying multiple permissions as a comma-separated string (e.g.,
+`'DELETE,INSERT,SELECT'`) will cause an error similar to:
+
+```text
+Cannot bind argument to parameter 'ReferenceObject' because it is null.
+```
+
+**Incorrect usage:**
+
+<!-- markdownlint-disable MD013 - Line length -->
+```powershell
+Permission = @(
+    DSC_DatabaseObjectPermission {
+        State      = 'Grant'
+        Permission = 'DELETE,INSERT,SELECT' # This will fail - multiple permissions in single string
+    }
+)
+```
+<!-- markdownlint-enable MD013 - Line length -->
+
+**Correct usage:**
+
+```powershell
+Permission = @(
+    DSC_DatabaseObjectPermission {
+        State      = 'Grant'
+        Permission = 'DELETE'
+    }
+    DSC_DatabaseObjectPermission {
+        State      = 'Grant'
+        Permission = 'INSERT'
+    }
+    DSC_DatabaseObjectPermission {
+        State      = 'Grant'
+        Permission = 'SELECT'
+    }
+)
+```
+
 All issues are not listed here, see [here for all open issues](https://github.com/dsccommunity/SqlServerDsc/issues?q=is%3Aissue+is%3Aopen+in%3Atitle+SqlDatabaseObjectPermission).