CustomCode Readonly field not working

Hello Everyone,

My custom code readonly textfield is not working on Version 7.13.1 but it was working before on my SuiteCRM v7.11.x.

'name' => 'document_name',
'customCode' => '<input name="document_name" id="document_name" type="text"  value="{$fields.document_name.value}" readonly="readonly">',