Throwing RandomDataGeneratorException instead of None.get

[yoohaemin]

Fix #6

[codecov]

Codecov Report

Merging #7 into master will increase coverage by 2.23%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
+ Coverage   82.14%   84.37%   +2.23%     
==========================================
  Files           5        5              
  Lines          28       32       +4     
  Branches        1        1              
==========================================
+ Hits           23       27       +4     
  Misses          5        5

Impacted Files	Coverage Δ
...omdatagenerator/magnolia/RandomDataGenerator.scala	100% <100%> (ø)	⬆️

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[DanielaSfregola]

Hi @yoo-haemin,
thanks for contributing!

LGTM ;)