code: public void setTheme(final JavascriptResourceReference theme) {
  		if (this.theme != null || this.themeUrl != null) {
  			throw new IllegalStateException(
  					"A theme can only be defined once. Calling different setTheme methods is not allowed!");
  		}
  		this.themeReference = theme;
  	}
docs: Sets the theme for this chart by specifying a reference to a javascript
  file containing the theme. The javascript file must contain the following
  code: <pre><code>
  Highcharts.setOptions(myOptions);
  </code></pre> where <code>myOptions</code> is a JSON representation of
  the theme options.
  
  A theme can only be set via one setTheme method. An
  {@link IllegalStateException} will be thrown if you call two setTheme
  methods.
  
  @see <a
  href="http://www.highcharts.com/demo">http://www.highcharts.com/demo</a>
  @param theme
  reference to a javascript file containing a theme.