added new TODO that the impl isn't as complete as it could be

org.springframework.expression/src/main/java/org/springframework/expression/spel/ast/OperatorPlus.java

@@ -26,6 +26,7 @@ public class OperatorPlus extends Operator {
 		super(payload);
 	}
 
+	// TODO OperatorPlus is lacking a bit on implementation...
 	@Override
 	public Object getValue(ExpressionState state) throws EvaluationException {
 		SpelNode leftOp = getLeftOperand();