Add Grid type to Switch Node, and SDF Grid Booleans handle no data input without error.

Hopefully a simple one... Would be hugely helpful for Switch node also handle Grid type. Secondly, make SDF Grid Booleans handle properly when no-data comes in on one of the inputs (ie from a switch). Presently errors and generates nothing. ie SDF Grid Boolean Difference... input 1 with grid, input 2 empty will result in input 1 being result.

Thanks!!