fix static analysis warnings by SonarQube

Warning list: https://sonarqube.ow2.org/project/issues?id=fr.inria.gforge.spoon%3Aspoon-core&resolved=false&types=BUG

I am using IDEA checkers to improve our code base but, at the same time some Sonar defects are solved as well (some checkers overlap).

I am going to fix all true positives on SonarQube on regular basis.

Today (2018-07-16) I am starting with 2076 issues to fix.

One more time I would like to get labels:
- code inspection (yellow) - to mark IDEA inspections
- sonarqube (orange) - to mark SonarQube inspections

to manage PRs with fixes. Also it would be change color of "bug" to RED :)

"refactor" label is better suited for refactoring of pure functionality (for instance: rework parser to support syntax X).

Review the linked SonarQube warning list and compare its findings with the IDEA checkers mentioned in the issue. Begin by separating true positives from overlapping inspections, then track fixes through the requested code inspection and sonarqube labels; completion would require addressing the identified true-positive warnings.

Written by the indexing model from the issue text.