code: @NonNull
      public static <T> T nonNull(@Nullable T obj, String paramName) {
          if (obj == null) {
              throw new IllegalArgumentException(String.format(
                      "'%s' must not be null", paramName));
          }
          return obj;
      }
docs: Asserts that the given object is non null.
  
  @param <T> Type of the object to test.
  @param obj The object to test.
  @param paramName The name of the parameter (used for exception message).
  @return The object.
  @throws IllegalArgumentException If {@code obj} is null.