A new check for -> on ManagedTypes.

inc/ErrorNo.h

@@ -45,6 +45,9 @@ enum PanicCode{
     MICROBIT_OOM = 20, 
 
     // Corruption detected in the micro:bit heap space
-    MICROBIT_HEAP_ERROR = 30 
+    MICROBIT_HEAP_ERROR = 30,
+
+    // Dereference of a NULL pointer through the ManagedType class,
+    MICROBIT_NULL_DEREFERENCE = 40,
 };
 #endif

inc/ManagedType.h

@@ -103,6 +103,8 @@ public:
      * x->m(); // resolves to T::m
      */
     T* operator->() {
+        if (object == NULL)
+            panic(MICROBIT_NULL_DEREFERENCE);
         return object;
     }