danielbachhuber 7e3414597f Meta: Allow empty strings to be set by Custom Fields meta box.
Because the REST API allows meta keys to have empty values, the Custom Fields meta box should permit the same behavior.

Props charlestonsw, soulseekah.
Fixes #43559.

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git-svn-id: http://core.svn.wordpress.org/branches/5.0@43640 1a063a9b-81f0-0310-95a4-ce76da25c4cd
2018-10-23 18:56:38 +00:00
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