optimize code and reduce code cyclomatic complexity

[tylitianrui]

• With pull requests:
  • Open your pull request against master
  • Your pull request should have no more than two commits, if not you should squash them.
  • It should pass all tests in the available continuous integration systems such as TravisCI.
  • You should add/modify tests to cover your proposed code changes.
  • If your pull request contains a new feature, please document it on the README.

[codecov]

Codecov Report

Merging #2737 (df4bebe) into master (97a32b1) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2737      +/-   ##
==========================================
- Coverage   98.69%   98.69%   -0.01%     
==========================================
  Files          41       41              
  Lines        2074     2072       -2     
==========================================
- Hits         2047     2045       -2     
  Misses         15       15              
  Partials       12       12              

Impacted Files	Coverage Δ
binding/form.go	100.00% <100.00%> (ø)
debug.go	100.00% <100.00%> (ø)

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[thinkerou]

lgtm