@sym/{ctranspose,transpose}: *transpose does not work on None

[alexvong243f]

I run into the following issues while improving #1194.

Let none = pycall_sympy__ ('return None').

Then both none.' and none' give error: Python exception: AttributeError: 'NoneType' object has no attribute...

I think both none.' and none' should evaluate to none. WDYT?

[cbm755]

I guess that's right, especially if that is convenient for other code. I'm not really concerned about them being errors either: anyone hitting this In Real Life has likely had something go wrong...

But again, I suspect you need it for other reasons...

[alexvong243f]

Yep, we need this for our 2D-sym-compatible functions otherwise tests will fail. I think none should have similar semantics as nan so it won't be too hard to fix / test.