fix add notebook but title is empty

app/src/main/java/org/houxg/leamonax/ui/Navigation.java

@@ -35,6 +35,7 @@ import org.houxg.leamonax.model.User;
 import org.houxg.leamonax.service.AccountService;
 import org.houxg.leamonax.service.NotebookService;
 import org.houxg.leamonax.utils.DisplayUtils;
+import org.houxg.leamonax.utils.ToastUtils;
 import org.houxg.leamonax.widget.AlphabetDrawable;
 import org.houxg.leamonax.widget.TriangleView;
 
@@ -297,8 +298,13 @@ public class Navigation {
                         .setPositiveButton(R.string.confirm, new DialogInterface.OnClickListener() {
                             @Override
                             public void onClick(DialogInterface dialog, int which) {
-                                dialog.dismiss();
-                                addNotebook(mEdit.getText().toString(), parentNotebookId);
+                                String newName = mEdit.getText().toString();
+                                if (TextUtils.isEmpty(newName)) {
+                                    ToastUtils.show(mActivity, R.string.notebook_name_cant_be_empty);
+                                } else {
+                                    dialog.dismiss();
+                                    addNotebook(newName, parentNotebookId);
+                                }
                             }
                         })
                         .show();

app/src/main/res/values-zh/strings.xml

@@ -106,4 +106,5 @@
     <string name="leanote">蚂蚁笔记</string>
     <string name="conflict_occurs">糟糕，笔记冲突</string>
     <string name="host_example">登录接口地址将会是:\n%s/api/auth/login</string>
+    <string name="notebook_name_cant_be_empty">笔记本名称不能为空</string>
 </resources>

app/src/main/res/values/strings.xml

@@ -108,5 +108,6 @@
     <string name="generate_random_note">Generate random note</string>
     <string name="conflict_occurs">Oops! Conflicts occurs</string>
     <string name="host_example">For example, login api will be:\n%s/api/auth/login</string>
+    <string name="notebook_name_cant_be_empty">Notebook\'s name can\'t be empty</string>
 
 </resources>