determine if this tree node is empty . description : check if this tree node contains a value . concurrency issues : - preconditions : - postconditions : - concode_field_sep EvaluationTree _tRight concode_elem_sep EvaluationTree _tLeft concode_elem_sep Object _oNode concode_field_sep String createSpaces concode_elem_sep String toString concode_elem_sep void toString concode_elem_sep boolean isLeaf
boolean function ( ) { return _oNode == null ; }