code: public static <T> T requireNonNull(T value, String parameterName) {
          if (value == null) {
              throw new NullPointerException(parameterName + " must not be null");
          }
          return value;
      }
docs: Ensures that the argument is non-null.
  
  @param <T>  the value type
  @param value  the value to check
  @param parameterName  the name of the parameter
  @return the checked non-null value
  @throws NullPointerException if the value is null