code: public static String getRendererOverride(final String classname) {
  		if (StringUtils.isBlank(classname)) {
  			throw new IllegalArgumentException("classname cannot be blank.");
  		}
  
  		return get().getString(RENDERER_OVERRIDE_PREFIX + classname);
  	}
docs: The overridden renderer class for the given fully qualified classname.
  
  @param classname the fully qualified classname of the WComponent to check for an overridden renderer.
  @return the parameter value, else null if not set.