refactoring: fixed sonarlint warnings

src/main/java/de/deadlocker8/budgetmaster/Main.java

...a/de/deadlocker8/budgetmaster/advices/SettingsAdvice.java

...in/java/de/deadlocker8/budgetmaster/backup/GitHelper.java

...a/de/deadlocker8/budgetmaster/backup/LocalBackupTask.java

...e/deadlocker8/budgetmaster/backup/LocalGitBackupTask.java

...adlocker8/budgetmaster/categories/CategoryController.java

.../deadlocker8/budgetmaster/categories/CategoryService.java

...a/de/deadlocker8/budgetmaster/charts/ChartController.java

...locker8/budgetmaster/controller/DatePickerController.java

.../deadlocker8/budgetmaster/database/DatabaseParser_v3.java

...de/deadlocker8/budgetmaster/database/DatabaseService.java

...eadlocker8/budgetmaster/database/legacy/LegacyParser.java

.../deadlocker8/budgetmaster/filter/FilterConfiguration.java

.../de/deadlocker8/budgetmaster/filter/FilterController.java

src/main/java/de/deadlocker8/budgetmaster/images/Image.java

...dlocker8/budgetmaster/reports/ReportGeneratorService.java

.../budgetmaster/reports/settings/ReportSettingsService.java

...de/deadlocker8/budgetmaster/settings/SettingsService.java

.../budgetmaster/transactions/TransactionSpecifications.java

...ker8/budgetmaster/unit/TransactionSpecificationsTest.java