code: public boolean registerUser(String username, String email,
              String password) {
          if (((username == null) && (email == null)) || (password == null)) {
              return false;
          }
          Object[] methodArgs = new Object[1];
          Map<String,Object> options = new HashMap<>();
          methodArgs[0] = options;
          if (username != null) {
              options.put("username", username);
          }
          if (email != null) {
              options.put("email", email);
          }
          options.put("password", password);
          getDDP().call("createUser", methodArgs, new DDPListener() {
              @Override
              public void onResult(Map<String, Object> jsonFields) {
                  handleLoginResult(jsonFields);
              }
          });
          return true;
      }
docs: Register's user into Meteor's accounts-password system
  @param username user's username (this or email has to be specified)
  @param email user's email (this or username has to be specified)
  @param password password
  @return true if create user called