code: public void toMatch(Pattern pattern) {
  		Arguments.ensureNotNull(pattern, "pattern cannot be null");
  		expectNotNull(this.getValue(), "Expected null to match '%s'", pattern.pattern());
  		expectTrue(pattern.matcher(this.getValue()).matches(),
  				"Expected '%s' to match '%s'", this.getValue(), pattern.pattern());
  	}
docs: Checks if the stored {@code String} matches a regular expression.
  <p>This method throws an {@code AssertionError} if
  <ul>
  <li>the stored {@code String} does not match the passed {@code pattern}</li>
  <li>the stored {@code String} is {@code null}</li>
  </ul>
  @param pattern the {@code Pattern} representing the regular expression
  @throws java.lang.IllegalArgumentException if {@code pattern} is {@code null}.