fix: filter_dict works with zero and empty str

[numb3r3]

No description provided.

[codecov]

Codecov Report

Merging #332 (0bf12c8) into main (1e7ba61) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #332   +/-   ##
=======================================
  Coverage   86.19%   86.19%           
=======================================
  Files         134      134           
  Lines        6316     6316           
=======================================
  Hits         5444     5444           
  Misses        872      872           

Flag	Coverage Δ
docarray	86.19% <100.00%> (ø)

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Impacted Files	Coverage Δ
docarray/__init__.py	100.00% <100.00%> (ø)
docarray/helper.py	76.66% <100.00%> (ø)

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