Add null checks for textfield texts

[mfl28]

• Adds null-checks for textfield commit-events.

Fixes #109.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (086724c) 86.53% compared to head (de38526) 86.46%.

Files	Patch %	Lines
...mfl28/boundingboxeditor/controller/Controller.java	44.44%	1 Missing and 4 partials ⚠️
...ngboxeditor/ui/settings/InferenceSettingsView.java	20.00%	0 Missing and 4 partials ⚠️
.../mfl28/boundingboxeditor/ui/TagScrollPaneView.java	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #110      +/-   ##
============================================
- Coverage     86.53%   86.46%   -0.08%     
  Complexity     1482     1482              
============================================
  Files            95       95              
  Lines          5928     5933       +5     
  Branches        531      534       +3     
============================================
  Hits           5130     5130              
  Misses          527      527              
- Partials        271      276       +5     

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

72.3% Coverage
0.0% Duplication