Misleading error in org.apache.activemq.transport.stomp.ProtocolConverter

From time to time I see the following log line for STOMP: 

2018-07-17 07:31:22,204 | WARN  | Exception occurred processing: <Unknown> -> org.apache.activemq.transport.stomp.ProtocolException: No subscription matched. | org.apache.activemq.transport.stomp.ProtocolConverter | ActiveMQ NIO Worker 1186

The misleading part is "<Unknown>", the unknown is suppose to be the STOMP's action word (SEND, SUBSCRIBE etc). 

The problem seems to be 

 org.apache.activemq.transport.stomp.ProtocolConverter.safeGetAction()

that is comparing the STOMP action word with constants defined in 

org.apache.activemq.transport.stomp.ProtocolConverter.Stomp.Commands

But for subscribe and unsubscribe the constants are defined as "SUB" and "UNSUB" which does not match the actual STOMP action verbs.