docs: warn when using defaultPopulate on collections with uploads e…

…nabled (#10138)

When `defaultPopulate` is enabled without specifying `filename: true`
and `url: true` for collections with an upload field. The upload will
not have a valid URL when returned from Payload APIs and will instead be
returned with a value of `null`

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

docs/queries/select.mdx

@@ -137,6 +137,11 @@ export const Pages: CollectionConfig<'pages'> = {
 }
 ```
 
+<Banner type="warning">
+  <strong>Important:</strong>
+  When using `defaultPopulate` on a collection with [Uploads](/docs/fields/upload) enabled and you want to select the `url` field, it is important to specify `filename: true` as well, otherwise Payload will not be able to construct the correct file URL, instead returning `url: null`.
+</Banner>
+
 ## populate
 
 Setting `defaultPopulate` will enforce that each time Payload performs a "population" of a related document, only the fields specified will be queried and returned. However, you can override `defaultPopulate` with the `populate` property in the Local and REST API: