REPORT-26263 切换远程目录到tomcat，放置一段时间切回本地，出现切换失败的弹窗，实际切换成功

修复 npe 。

designer-form/src/main/java/com/fr/design/mainframe/JForm.java

@@ -543,8 +543,12 @@ public class JForm extends JTemplate<Form, FormUndoState> implements BaseJForm<F
      */
     public boolean canUndo() {
         //报表块最多撤销至编辑报表块的第一步，不能撤销表单中的操作
-        boolean inECUndoForm = undoState.getFormReportType() == BaseUndoState.STATE_BEFORE_FORM_REPORT && formDesign.isReportBlockEditing();
+        boolean inECUndoForm = undoState != null
-        return !inECUndoForm && this.getUndoManager().canUndo();
+                && undoState.getFormReportType() == BaseUndoState.STATE_BEFORE_FORM_REPORT
+                && formDesign.isReportBlockEditing();
+        return !inECUndoForm
+                && this.getUndoManager() != null
+                && this.getUndoManager().canUndo();
     }
 
     // 返回当前的body，

designer-form/src/test/java/com/fr/design/mainframe/JFormTest.java

@@ -0,0 +1,20 @@
+package com.fr.design.mainframe;
+
+import org.easymock.EasyMock;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class JFormTest {
+    
+    @Test
+    public void testRun() {
+    
+        JForm mockForm = EasyMock.partialMockBuilder(JForm.class).addMockedMethod("getUndoManager").createMock();
+        try {
+            mockForm.canUndo();
+        } catch (Exception e) {
+            Assert.fail();
+        }
+    }
+    
+}