private String getRegExFilterNodeValue(final Document doc) {
		Node filterNode = this.getFirstLevelNodeByTag(doc, FILTER_TAG);
		if (filterNode == null) {
			return null;
		}
		Node regExFilterNode = this.getNodeByTagInNode(filterNode, REGEX_FILTER_TAG);
		if (regExFilterNode == null) {
			return null;
		}
		String value = this.getNodeValue(regExFilterNode);
		if (value.isEmpty()) {
			value = null;
		}
		return value;
	}