message: null exception corrected by separating summands of first line number calculation in separated brackets with || 0
diff: @@ -62,9 +62,8 @@ export class CodeKataComponent implements OnInit {
  });
  this.testEditor.setOptions({
  maxLines: 9999,
  - firstLineNumber: (
  - (this.codeKataUnit.definition.split('\n').length
  - + this.codeEditor.text.split('\n').length) || 0) + 1,
  + firstLineNumber: ((this.codeKataUnit.definition.split('\n').length || 0) +
  + (this.codeEditor.text.split('\n').length || 0) + 1),
  });
  }
  