Hive Items throw an Exception on ToString

[mkommend]

HiveItems constructed by default ctor throw NullReferenceException in the ToString method.

 var item = new OptmizerTask();
 item.ToString() // throws exception

This happens by more than one item and so the best way would be to test the functionality in a UnitTest and correct the according classes.

[ascheibe]

r7530 check if the item in ItemTask and OptimizerTask is null

[ascheibe]

r7532

• tried to clean up ItemTask/EngineTask overrides without breaking anything
• added a unit test to check if ToString methods of IItems work
• fixed ToString method of the Hive Plugin dto

Just a quick note: The ItemTask/OptimizerTask/EngineTask classes should be refactored in the future when there is the next compatibility break in Hive. ItemTask should not inherit NamedItem as the EngineTask does not contain a NamedItem and therefore doesn't know how to implement those members appropriately.