code: @Factory
    public static Matcher<String> notEmptyString() {
      return new CustomTypeSafeMatcher<String>("not empty") {
        @Override
        protected boolean matchesSafely(String s) {
          return !s.isEmpty();
        }
      };
    }
docs: A matcher matching non-null and non-empty strings
  
  Example:
  <pre>assertThat("this is not an empty string", notEmptyString())</pre>
  
  @return
  matcher for a not empty string