Don't hide null issues

[BraisGabin]

getResource and getResourceAsStream can return a null value But they are java functions so the compiler doesn't complain about it.

This PR only shows clearly in the code where we could have a NullPointerException.

[codecov]

Codecov Report

Merging #4313 (a7f2a2d) into main (d257c2a) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               main    #4313   +/-   ##
=========================================
  Coverage     84.22%   84.22%           
  Complexity     3258     3258           
=========================================
  Files           472      472           
  Lines         10309    10309           
  Branches       1820     1820           
=========================================
  Hits           8683     8683           
  Misses          666      666           
  Partials        960      960           

Impacted Files	Coverage Δ
...lab/arturbosch/detekt/core/config/DefaultConfig.kt	100.00% <100.00%> (ø)
...bosch/detekt/core/tooling/DefaultConfigProvider.kt	80.00% <100.00%> (ø)
...n/io/github/detekt/report/html/HtmlOutputReport.kt	95.55% <100.00%> (ø)

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