Fix issues as noted by SonarLint + field name in repository classes

"@Override" should be used on overriding and implementing methods
"Preconditions" and logging arguments should not require evaluation
"static" base class members should not be accessed via derived types
Collection.isEmpty() should be used to test for emptiness
Constructors of an "abstract" class should not be declared "public"
Mutable fields should not be "public static"
Pattern Matching for "instanceof" operator should be used instead of simple "instanceof" + cast
Redundant casts should not be used
Sections of code should not be commented out
String literals should not be duplicated
Unused assignments should be removed