code: void parameter(Object value) {
          // TODO check on supported types?
          if (value instanceof Observable)
              throw new IllegalArgumentException(
                      "use parameters() method not the parameter() method for an Observable");
          parameters(Observable.just(value));
      }
docs: Appends a parameter to the parameter list for the query. If there are
  more parameters than required for one execution of the query then more
  than one execution of the query will occur.
  
  @param value