public String getString(String key) {
        Object o = getMap().get(key);
        if(o == null) {
            return null;
        } else {
            return o.toString();
        }
    }
Helper function to get a String from the Annotation. This function will simply call <code>toString()</code> on the
object saved in the Annotation or return null if the object is null;
container-search/src/main/java/com/yahoo/text/interpretation/Annotations.java