fix(handsontable): 当fees等属性为null时，取值报错问题

handsontable/package.json

@@ -10,7 +10,7 @@
     "url": "https://github.com/handsontable/handsontable/issues"
   },
   "author": "Handsoncode <hello@handsontable.com>",
-  "version": "6.3.10",
+  "version": "6.3.11",
   "browser": "dist/handsontable.js",
   "main": "commonjs/index.js",
   "module": "es/index.js",

handsontable/src/dataMap.js

@@ -520,7 +520,7 @@ DataMap.prototype.get = function(row, prop) {
     for (let i = 0, ilen = sliced.length; i < ilen; i++) {
       out = out[sliced[i]];
 
-      if (typeof out === 'undefined') {
+      if (typeof out === 'undefined' || out === null) {
         return null;
       }
     }