String toTest =
        MoreObjects.toStringHelper(new TestClass())
            .omitEmptyValues()
            .omitEmptyValues()
            .add("field1", "Hello")
            .omitEmptyValues()
            .add("field2", "Googley")
            .omitEmptyValues()
            .add("field3", "World")
            .toString();

     * Collection}s, {@code Map}s, optionals (including Guava's), and arrays.
     *
     * @since NEXT
     */
    @CanIgnoreReturnValue
    public ToStringHelper omitEmptyValues() {
      omitEmptyValues = true;
      return this;
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format. If {@code value}