snaker-core/src/main/java/org/snaker/engine/model/ProcessModel.java
public StartModel getStart() {
		for(NodeModel node : nodes) {
			if(node instanceof StartModel) {
				return (StartModel)node;
			}
		}
		return null;
	}
public StartModel getStart() {
		for(NodeModel node : nodes) {
			if(node instanceof StartModel) {
				return (StartModel)node;
			}
		}
		return null;
	}
获取process定义的start节点模型
@return