Less dependant on the class name
Consistent indentation and new-lines according to psr-2
Consistent docblocks and typehinting
Removed unused properties
Consistent use of square bracket notation
Directly return result
isset can handle multiple arguments
Simpler string interpolation
Typehinting
Put input validation up front and the ifs are no longer necessary
Simpler .gitignore. IDE ignore should go in global .gitignore