Handle null value safely in case-insensitive filter

[xwk]

Fix the issue described in #934

Basically if the value is null, return empty string directly instead of call .toString()

[zekeshearer]

I have this same issue on dash 2.8.1. @alexcjohnson or other maintainer, could you review this?

[alexcjohnson]

Oh thanks @zekeshearer - I had missed this PR as this repo is obsolete. I think perhaps it was created right around when we merged Dash Table into the main Dash repo.

So we can recreate it in the Dash repo. Definitely we should fix this, but I’m not sure if empty string is the right fallback, would we be better off leaving it as its non-string value so it doesn’t match an explicit empty string?

Lastly it deserves a test case.

[bparzonz]

Hi, this appears to still be an issue. Is it being addressed elsewhere?