code: public void assertMatches(@Nullable Description description, @Nullable String actual, @Nonnull String regex) {
      checkNotNull(regex);
      assertMatches(description, actual, Pattern.compile(regex));
    }
docs: Verifies that the <em>actual</em> {@code String} matches the given regular expression.
  
  @param description the description of the <em>actual</em> {@code String}.
  @param actual the <em>actual</em> {@code String}.
  @param regex the regular expression to which the <em>actual</em> {@code String} is to be matched.
  @throws NullPointerException if the given regular expression is {@code null}.
  @throws PatternSyntaxException if the regular expression's syntax is invalid.
  @throws AssertionError if the <em>actual</em> {@code String} is {@code null}.
  @throws AssertionError if the <em>actual</em> {@code String} does not match the given regular expression.