dev(hansbug): try fix the problem in mapping's function

[HansBug]

Description

Fix the bug in issue #21

Check List

• merge the latest version source branch/repo, and resolve all the conflicts
• pass style check
• pass all the tests

[codecov]

Codecov Report

Merging #22 (89893df) into main (8a78ab2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #22   +/-   ##
=======================================
  Coverage   99.19%   99.19%           
=======================================
  Files          34       34           
  Lines        1855     1861    +6     
=======================================
+ Hits         1840     1846    +6     
  Misses         15       15           

Flag	Coverage Δ
unittests	99.19% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
treevalue/tree/tree/functional.pyx	100.00% <100.00%> (ø)

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