code: private void registerCommand(String cmdOwner, RegisteredCommand cmd) {
          // Add to owner map in RESTCatalog.
          Map<String, RESTCommand> nameMap = getCmdNameMap(cmdOwner);
          String cmdName = cmd.getName();
          RESTCommand oldCmd = nameMap.put(cmdName, cmd);
          if (oldCmd != null) {
              throw new RuntimeException("Duplicate REST command with same owner/name: " +
                                         "owner=" + cmdOwner + ", name=" + cmdName +
                                         ", [1]=" + cmd + ", [2]=" + oldCmd); 
          }
          
          // Add to local evaluation map.
          Map<HttpMethod, SortedSet<RegisteredCommand>> evalMap = getCmdEvalMap(cmdOwner);
          for (HttpMethod method : cmd.getMethods()) {
              SortedSet<RegisteredCommand> methodSet = evalMap.get(method);
              if (methodSet == null) {
                  methodSet = new TreeSet<>();
                  evalMap.put(method, methodSet);
              }
              if (!methodSet.add(cmd)) {
                  throw new RuntimeException("Duplicate REST command: owner=" + cmdOwner +
                                             ", name=" + cmdName + ", commmand=" + cmd); 
                  
              }
          }
      }
docs: Register the given command and throw if is a duplicate name or command.