code: public static String notEmpty(String value, String variableName) {
          if (value == null) {
              throw new NullPointerException("ERROR: Trying to use String with null " + variableName);
          }
          if (value.isEmpty()) {
              throw new IllegalArgumentException("ERROR: Illegal empty string for " + variableName);
          }
          return value;
      }
docs: Validates if provided value is non-null and non-empty.
  
  @param value the string to validate
  @param variableName name of the variable to include in error messages
  @return the value parameter if valid, throws an exception otherwise