Fix exception

[zhiqwang]

No description provided.

[codecov]

Codecov Report

Merging #183 (cfd0982) into master (c9b5b6f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #183   +/-   ##
=======================================
  Coverage   96.48%   96.48%           
=======================================
  Files          10       10           
  Lines         598      598           
=======================================
  Hits          577      577           
  Misses         21       21           

Flag	Coverage Δ
unittests	96.48% <ø> (ø)

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