Fix: Methods can be static

[localheinz]

This PR

• declares methods which can be static as static

[codecov]

Codecov Report

Merging #183 into 1.x will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                1.x     #183   +/-   ##
=========================================
  Coverage     82.68%   82.68%           
  Complexity       37       37           
=========================================
  Files             2        2           
  Lines           179      179           
=========================================
  Hits            148      148           
  Misses           31       31

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