fix npe

hutool-core/src/main/java/cn/hutool/core/lang/tree/TreeUtil.java

@@ -134,14 +134,14 @@ public class TreeUtil {
 			return node;
 		}
 
-		//fix NPE
-		if(null == node.getChildren()) {
+		final List<Tree<T>> children = node.getChildren();
+		if(null == children) {
 			return null;
 		}
 		
 		// 查找子节点
 		Tree<T> childNode;
-		for (Tree<T> child : node.getChildren()) {
+		for (Tree<T> child : children) {
 			childNode = child.getNode(id);
 			if (null != childNode) {
 				return childNode;

hutool-core/src/test/java/cn/hutool/core/lang/tree/TreeSearchTest.java

@@ -0,0 +1,37 @@
+package cn.hutool.core.lang.tree;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class TreeSearchTest {
+	static List<TreeNode<Long>> all_menu=new ArrayList<>();
+	static {
+		/*
+		 * root
+		 *    /module-A
+		 *    	   /module-A-menu-1
+		 *    /module-B
+		 *    	   /module-B-menu-1
+		 *    	   /module-B-menu-2
+		 */
+		all_menu.add(new TreeNode<>(1L, 0L, "root", 0L));
+		all_menu.add(new TreeNode<>(2L,1L,"module-A",0L));
+		all_menu.add(new TreeNode<>(3L,1L,"module-B",0L));
+		all_menu.add(new TreeNode<>(4L,2L,"module-A-menu-1",0L));
+		all_menu.add(new TreeNode<>(5L,3L,"module-B-menu-1",0L));
+		all_menu.add(new TreeNode<>(6L,3L,"module-B-menu-2",0L));
+	}
+
+	@Test
+	public void searchNode() {
+		List<Tree<Long>> treeItems=TreeUtil.build(all_menu, 0L);
+
+		Tree<Long> tree=treeItems.get(0);
+		Tree<Long> searchResult=tree.getNode(3L);
+
+		Assert.assertEquals("module-B", searchResult.getName());
+	}
+}