code: public static String checkNotBlank(String str, String message) {
          checkNotNull(str, message);
          checkArgument(Strings.isNotBlank(str), message);
          return str;
      }
docs: Checks that the given string is not blank and throws a customized
  {@link NullPointerException} if it is {@code null}, and a customized
  {@link IllegalArgumentException} if it is empty or whitespace. Intended for doing parameter
  validation in methods and constructors, e.g.:
  <blockquote><pre>
  public void foo(String text) {
  checkNotBlank(text, "The text must not be null, empty or whitespace.");
  }
  </pre></blockquote>
  
  @param str the string to check for being blank
  @param message the detail message to be used in the event that an exception is thrown
  @return {@code str} if not {@code null}
  @throws NullPointerException if {@code str} is {@code null}
  @throws IllegalArgumentException if {@code str} is empty or whitespace