Error: Undefined index (fix)

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ERROR
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Notice: Undefined index: field_required in D:\HTTP\www\wp-content\plugins\custompress\ui-admin\display-custom-fields.php on line 29

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ORIGINAL
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$required = ($custom_field['field_required'] == 1) ? 'required' : ''; //required field class

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FIX
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if (isset($custom_field['field_required']))
$required = ($custom_field['field_required'] == 1) ? 'required' : ''; //required field class
else
$required = ''; //not required