Expand Object component doesn't skip null inputs in a list

[daviddekoning]

Step 0:

• [x] I've read the contribution guidelines!

Expected Behaviour

When the input list of SpeckleObjects contains some null values, there should still be output corresponding to the valid inputs.

Actual Behaviour

If a list of SpeckleObjects is passed in, and some of them are null, the whole component fails and produces no output (note that the component runs once the null values are filtered out):

Affected Projects

This is a GH specific issue.

Reproduction Steps & System Config (win, osx, web, etc.)

This is occuring on Windows 10, with Rhino 6 and Speckle-v1.8.24.320.

Proposed Solution (if any)

A null check here will likely be a good starting point: https://github.com/speckleworks/SpeckleRhino/blob/059982950394abc926bdacfd435754ace998d307/SpeckleGrasshopper/ObjectCreation/ExpandObject.cs#L82