Emitted when an array has a key more than once
<?php $arr = [ 'a' => 'one', 'b' => 'two', 'c' => 'this text will be overwritten by the next line', 'c' => 'three', ];
How to fix
Remove the offending duplicates:
<?php $arr = [ 'a' => 'one', 'b' => 'two', 'c' => 'three', ];
The first matching
'c' key was removed to prevent a change in behaviour (any new duplicate keys overwrite the values of previous ones).