Tree: get prop from data if not specified in `props`

examples/docs/en-US/tree.md

@@ -878,7 +878,7 @@ Only one node among the same level can be expanded at one time.
 | --------- | ---------------------------------------- | ------ | --------------- | ------- |
 | label     | specify which key of node object is used as the node's label | string, function(data, node) | —               | —       |
 | children | specify which node object is used as the node's subtree | string, function(data, node) | —               | —       |
-| disabled | specify which node's checkbox disabled |  boolean, function(data, node) | —    | —    |
+| disabled | specify which key of node object represents if node's checkbox is disabled |  boolean, function(data, node) | —    | —    |
 
 ### Method
 `Tree` has the following method, which returns the currently selected array of nodes.

examples/docs/zh-CN/tree.md

@@ -877,7 +877,7 @@
 | -------- | ----------------- | ------ | ---- | ---- |
 | label    | 指定节点标签为节点对象的某个属性值 | string, function(data, node) | —    | —    |
 | children | 指定子树为节点对象的某个属性值 | string, function(data, node) | —    | —    |
-| disabled | 指定节点选择框是否禁用 |  boolean, function(data, node) | —    | —    |
+| disabled | 指定节点选择框是否禁用为节点对象的某个属性值 |  boolean, function(data, node) | —    | —    |
 
 ### 方法
 `Tree` 拥有如下方法，返回目前被选中的节点数组：

packages/tree/src/model/node.js

@@ -68,7 +68,8 @@ const getPropertyFromData = function(node, prop) {
   } else if (typeof config === 'string') {
     return data[config];
   } else if (typeof config === 'undefined') {
-    return '';
+    const dataProp = data[prop];
+    return dataProp === undefined ? '' : dataProp;
   }
 };