Fix the type casting in labels

[zhiqwang]

Fix #220

[codecov]

Codecov Report

Merging #221 (191f234) into main (b8d845d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #221   +/-   ##
=======================================
  Coverage   96.98%   96.98%           
=======================================
  Files          10       10           
  Lines         631      631           
=======================================
  Hits          612      612           
  Misses         19       19           

Flag	Coverage Δ
unittests	96.98% <ø> (ø)

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