private applyChanges(changes: KeyValueChanges<string, L.Layer>, addFn: (layer: L.Layer, name: string) => void): LeafletControlLayersChanges {
		let results: LeafletControlLayersChanges = new LeafletControlLayersChanges();

		if (null != changes) {

			changes.forEachChangedItem((c) => {
				this.layersControl.removeLayer(c.previousValue);
				addFn.call(this.layersControl, c.currentValue, c.key);
				results.layersChanged++;
			});
			changes.forEachRemovedItem((c) => {
				this.layersControl.removeLayer(c.currentValue);
				results.layersRemoved++;
			});
			changes.forEachAddedItem((c) => {
				addFn.call(this.layersControl, c.currentValue, c.key);
				results.layersAdded++;
			});

		}

		return results;
	}

  transform<K, V>(
      input: null|{[key: string]: V, [key: number]: V}|Map<K, V>,
      compareFn: (a: KeyValue<K, V>, b: KeyValue<K, V>) => number = defaultComparator):
      Array<KeyValue<K, V>>|null {
    if (!input || (!(input instanceof Map) && typeof input !== 'object')) {
      return null;
    }

    if (!this.differ) {
      // make a differ for whatever type we've been passed in
      this.differ = this.differs.find(input).create();
    }

    const differChanges: KeyValueChanges<K, V>|null = this.differ.diff(input as any);

    if (differChanges) {
      this.keyValues = [];
      differChanges.forEachItem((r: KeyValueChangeRecord<K, V>) => {
        this.keyValues.push(makeKeyValuePair(r.key, r.currentValue !));
      });
      this.keyValues.sort(compareFn);
    }
    return this.keyValues;
  }

 private _applyChanges(changes: KeyValueChanges<string, string|number>): void {
   changes.forEachRemovedItem((record) => this._setStyle(record.key, null));
   changes.forEachAddedItem((record) => this._setStyle(record.key, record.currentValue));
   changes.forEachChangedItem((record) => this._setStyle(record.key, record.currentValue));
 }

			this.zone.runOutsideAngular(() => {

				changes.forEachChangedItem((c) => {
					this.layersControl.removeLayer(c.previousValue);
					addFn.call(this.layersControl, c.currentValue, c.key);
					results.layersChanged++;
				});
				changes.forEachRemovedItem((c) => {
					this.layersControl.removeLayer(c.previousValue);
					results.layersRemoved++;
				});
				changes.forEachAddedItem((c) => {
					addFn.call(this.layersControl, c.currentValue, c.key);
					results.layersAdded++;
				});

			});