code: public static String concatConsistentCase(String baseString, String addition) {
          boolean hasLowerCase = hasLowerCase(baseString);
          boolean hasUpperCase = hasUpperCase(baseString);
          if ((hasLowerCase && hasUpperCase) || (!hasLowerCase && !hasUpperCase)) { //mixed case || no letters
              return baseString + addition;
          } else if (hasLowerCase) {
              return baseString + addition.toLowerCase();
          } else {
              return baseString + addition.toUpperCase();
          }
      }
docs: Concatenates the addition string to the baseString string, adjusting the case of "addition" to match the base string.
  If the string is all caps, append addition in all caps. If all lower case, append in all lower case. If baseString is mixed case, make no changes to addition.