public String getString(String key) {
        String s = (String) get(key);
        if (s == null) {
            return null;
        }

        return s;
    }
Get a string from the settings.
<p>
If the key is not set, then null is returned.

@param key the key of a string setting
@return the corresponding value, or null if not set
jme3-core/src/main/java/com/jme3/system/AppSettings.java