@Override
  public String errorText() {
    return errorMessage;
  }
The exception thrown within
{@link com.google.protobuf.Service#callMethod(com.google.protobuf.Descriptors.MethodDescriptor, RpcController, com.google.protobuf.Message, RpcCallback)}
if any.
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/ServerRpcController.java