KotlinParseException on string concatenation in fix plugin

[Cheshiriks]

What's done:

• fixed null-safety in rule
  This pull request closes KotlinParseException on string concatenation #1181

[codecov]

Codecov Report

Merging #1183 (acdd40f) into master (2011aff) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #1183   +/-   ##
=========================================
  Coverage     84.64%   84.64%           
- Complexity     2517     2519    +2     
=========================================
  Files           103      103           
  Lines          7053     7055    +2     
  Branches       1898     1899    +1     
=========================================
+ Hits           5970     5972    +2     
  Misses          302      302           
  Partials        781      781           

Flag	Coverage Δ
unittests	84.64% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../ruleset/rules/chapter3/StringConcatenationRule.kt	75.51% <100.00%> (+0.51%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2011aff...acdd40f. Read the comment docs.