update

chip/zgpio.hpp

@@ -85,6 +85,8 @@ class ZGPIO {
   bool     setState(bool state);
   void     toggleState();
 
+  bool isNull() { return m_pin == PinNull; }
+
   Pin_t getPin() { return m_pin; }
 
   IRQn_Type     getEXTIIRQn();