code: public static String checkNotBlank(
              String str, String messageFormat, Object... messageArgs) {
          checkNotNull(str, messageFormat, messageArgs);
          checkArgument(Strings.isNotBlank(str), messageFormat, messageArgs);
          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, String id) {
  checkNotBlank(
  text,
  "The text for %s must not be null, empty or whitespace.",
  id);
  }
  </pre></blockquote>
  
  @param str the string to check for being blank
  @param messageFormat a {@link Formatter format} string for the detail message to be used in
  the event that an exception is thrown.
  @param messageArgs the arguments referenced by the format specifiers in the
  {@code messageFormat}
  @return {@code str} if not {@code null}
  @throws NullPointerException if {@code str} is {@code null}
  @throws IllegalArgumentException if {@code str} is empty or whitespace