Android studio ble蓝牙配对成功后，远距离断开蓝牙后，再回近距离搜索不到蓝牙名称也无法配对成功，是什么情况？
以下是报错信息
```java
E/TestSerice2: onConnectionStateChange fail-->（连接状态更改）0
D/BluetoothGatt: close()
D/BluetoothGatt: unregisterApp() - mClientIf=14
D/BluetoothGatt: cancelOpen() - device: 94:C9:60:**:**:**
W/BluetoothGatt: Unhandled exception in callback
java.lang.NullPointerException: Attempt to invoke virtual method 'android.bluetooth.BluetoothGatt android.bluetooth.BluetoothDevice.connectGatt(android.content.Context, boolean, android.bluetooth.BluetoothGattCallback)' on a null object reference
at com.example.myapplication.TestService2$3.onConnectionStateChange(TestService2.java:209)
at android.bluetooth.BluetoothGatt$1$4.run(BluetoothGatt.java:280)
at android.bluetooth.BluetoothGatt.runOrQueueCallback(BluetoothGatt.java:794)
at android.bluetooth.BluetoothGatt.access$400(BluetoothGatt.java:42)
at android.bluetooth.BluetoothGatt$1.onClientConnectionState(BluetoothGatt.java:275)
at android.bluetooth.IBluetoothGattCallback$Stub.onTransact(IBluetoothGattCallback.java:192)
at android.os.Binder.execTransactInternal(Binder.java:1028)
at android.os.Binder.execTransact(Binder.java:1001)
D/DecorView: showOrHideHighlightView: hasFocus=true; winMode=1; isMrgNull=true
