Merge pull request #5782 from sbueringer/pr-api-conventions-struct-po…

…inter

📖 API conventions: add note about when struct fields should be pointer

CONTRIBUTING.md

@@ -338,8 +338,11 @@ This project follows the [Kubernetes API conventions](https://github.com/kuberne
 
 Optional fields have the following properties:
 * An optional field MUST be marked with `+optional` and include an `omitempty` JSON tag.
-* Fields SHOULD be pointers if the nil and the zero values (by Go standards) have semantic differences.
-  * Note: This doesn't apply to map or slice types as they are assignable to `nil`.
+* Fields SHOULD be pointers if there is a good reason for it, for example:
+  * the nil and the zero values (by Go standards) have semantic differences.
+    * Note: This doesn't apply to map or slice types as they are assignable to `nil`.
+  * the field is of a struct type, contains only fields with `omitempty` and you want 
+    to prevent that it shows up as an empty object after marshalling (e.g. `kubectl get`) 
 
 #### Example