Deprecated function: explode(): Passing null to parameter of type string is deprecated

Then if you try to upload a file, you get the message "You can only upload: .", and nothing is uploaded.

No cardinality was changed (from the default 1, of the Article Image field) and I was trying to upload only 1 image (with acceptable dimensions).

Successfully reproduced the error locally and resolved the Deprecated function error.
Please refer to the attached patch. Thanks.