Add else condition when one of the element is null

src/bootstrap-table.js

@@ -1034,6 +1034,9 @@ class BootstrapTable {
             for (let i = 0; i < props.length; i++) {
               if (value[props[i]] !== null) {
                 value = value[props[i]]
+              } else {
+                value = null
+                break;
               }
             }
           } else {