RandomStringGenerator should be able to pass multiple ranges to .withinRange()

char [][]  ranges = {{'0','9'}};
RandomStringGenerator generator = new RandomStringGenerator.Builder().withinRange(ranges).build();

char [][]  ranges = {{'A','Z'}}; // or {{'A','Z'},{'a','z'}}
RandomStringGenerator generator = new RandomStringGenerator.Builder().withinRange(ranges).build();

char [][]  ranges = {{'0','9'},{'A','Z'},{'a','b'}};
RandomStringGenerator generator = new RandomStringGenerator.Builder().withinRange(ranges).build();