Fixes crash while copy paste of custom node.

- Nickname is not serialized while copying custom node and while pasting
it was trying to get it and hence crashed.
- Fixes http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4235
Merge pull request #2205 from sharadkjaiswal/MAGN-4235

Fixes crash while copy paste of custom node.