code: public static <E> E isNotNull(E argument, String argName) {
          if (argument == null) {
              throw new IllegalArgumentException(format("argument '%s' can't be null", argName));
          }
  
          return argument;
      }
docs: Tests if a string is not null.
  
  @param argument the string tested to see if it is not null.
  @param argName  the string name (used in message if an error is thrown).
  @return the string argument that was tested.
  @throws java.lang.IllegalArgumentException if the string is null.