Adding a verification of obj value if not an array so we don't try to use push on a empty string

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Checklist before requesting a review

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• [ x ] I have performed a self-review of my code.

Description

• It fixes Buggy dropdown won't close properly and doesn't set value correctly sometimes #1155
• Here is a brief description of what this PR does :
  It checks the value of the item that has multiple matches in obj to see if it's an empty string instead of an empty array (this can happen when a multi-value field is checked) in which case it's replaced by an empty array so the code doesn't bug when trying to push a value to a string.