Looks like the compatibility checker you are using reports a false positive here. This error does not exists, it thinks that the constant value on that line is defined as an array, when it's actually not. The plugin was tested from PHP 5.1.4 to PHP 7, you can safely use it without any error messages. This warning is incorrect.
Please note that compatibility checkers does not actually execute the code to check for errors, they just look for patterns, therefore produce many false positives: https://github.com/wpengine/phpcompat/wiki/ResultsBest,
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