@Override
  public VectorExpressionDescriptor.Descriptor getDescriptor() {

    // Descriptor is not defined because it takes variable number of arguments with different
    // data types.
    throw new UnsupportedOperationException("Undefined descriptor");
  }
Base class that supports conditional execution of the THEN/ELSE vector expressions of
a SQL IF statement.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/IfExprCondExprBase.java