@Override
  public boolean isOptional(int i) {
    return false;
  }
Checks if there is only one UdfMethod in the input {@link UdfMetadata}.
@param udfMetadata the metadata for a UDF.
@return true if there is only one udf method defined in the UdfMetadata.
        false otherwise.
samza-sql/src/main/java/org/apache/samza/sql/planner/Checker.java