Spring ManagedMap

@Override
@SuppressWarnings("unchecked")
public Object merge(@Nullable Object parent) {
    if (!this.mergeEnabled) {
        throw new IllegalStateException("Not allowed to merge when the 'mergeEnabled' property is set to 'false'");
    }
    if (parent == null) {
        return this;
    }
    if (!(parent instanceof Map)) {
        throw new IllegalArgumentException("Cannot merge with object of type [" + parent.getClass() + "]");
    }
    Map<K, V> merged = new ManagedMap<>();
    merged.putAll((Map<K, V>) parent);
    merged.putAll(this);
    return merged;
}