Collection node throws error that prevents build if connected mesh not defined in NGE

[PatrickRyanMS]

When building node geometry using a collection to instantiate a randomly selected mesh, if the blocks connected to the CollectionBlock are MeshBlock nodes that do not have a mesh assigned, the graph will not build due to not being able to read metadata from null. Being able to build a graph like this allows the user to assign meshes to the MechBlocks in the graph from code, but the graph needs to be built before meshes can be assigned in code.

Repro