[AL-2298] Fix bugs with None samples

[FayazRahman]

🚀 🚀 Pull Request

Checklist:

• My code follows the style guidelines of this project and the Contributing document
• I have commented my code, particularly in hard-to-understand areas
• I have kept the coverage-rate up
• I have performed a self-review of my own code and resolved any problems
• I have checked to ensure there aren't any other open Pull Requests for the same change
• I have described and made corresponding changes to the relevant documentation
• New and existing unit tests pass locally with my changes

Changes

[adolkhan]

was this throwing an error before if samples were none? If yes, can you pls add some tests?

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.04 🎉

Comparison is base (d721775) 84.71% compared to head (415aebc) 84.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2382      +/-   ##
==========================================
+ Coverage   84.71%   84.75%   +0.04%     
==========================================
  Files         323      323              
  Lines       36569    36591      +22     
==========================================
+ Hits        30980    31014      +34     
+ Misses       5589     5577      -12     

Flag	Coverage Δ
unittests	84.75% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
deeplake/util/casting.py	88.31% <ø> (ø)
deeplake/api/tests/test_none.py	100.00% <100.00%> (ø)
deeplake/core/chunk_engine.py	92.90% <100.00%> (+0.18%)	⬆️

... and 6 files with indirect coverage changes

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