code: public void assertLowerCase(Description description, Character actual) {
      assertNotNull(description, actual);
      if (!isLowerCase(actual)) {
        throw failures.failure(description, shouldBeLowerCase(actual));
      }
    }
docs: Asserts that the actual value is a lowercase character.
  
  @param description contains information about the assertion.
  @param actual the actual value.
  @throws AssertionError if the actual value is {@code null}.
  @throws AssertionError if the actual value is not a lowercase character.