public void mergeFrom(AppSettings other) {
        for (String key : other.keySet()) {
            if (!this.containsKey(key)) {
                put(key, other.get(key));
            }
        }
    }
Same as {@link #copyFrom(com.jme3.system.AppSettings) }, except
doesn't overwrite settings that are already set.

@param other  The AppSettings to merge the settings from
jme3-core/src/main/java/com/jme3/system/AppSettings.java