I solved it my self.
cmb2 -> includes -> CMB2_Field.php -> line 471
false === $cb
if the callback function is empty, it will return NULL
and because of you’re using false === $cb => return call_user_func( $cb, $meta_value, $this->args(), $this ); will be executed => return null.
Thanks
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This reply was modified 6 years, 9 months ago by wiloke.