ActionDispatch::Http::MimeNegotiation::InvalidType: "${#context[\"com.opensymphony.xwork2.dispatcher.httpservletresponse\"].addheader(\"keyvalue\"" is not a valid MIME type

ActionDispatch::Http::MimeNegotiation::InvalidType: "${#context[\"com.opensymphony.xwork2.dispatcher.httpservletresponse\"].addheader(\"keyvalue\"" is not a valid MIME type #2621