HID: Zero-initialize pointer members

I'm new to Arduino development, so I'm not sure if variable are zero-initialized by default. Regardless, it's often regarded good practice to explicitly zero-initialize pointers to reduce risk of treating uninitialized pointers as valid.

src/HID/HID.cpp

@@ -266,7 +266,7 @@ bool HID_::setup(USBSetup& setup)
 }
 
 HID_::HID_(void) : PluggableUSBModule(2, 1, epType),
-                   rootNode(NULL), descriptorSize(0),
+                   descriptorSize(0),
                    protocol(HID_REPORT_PROTOCOL), idle(1)
 {
 	epType[0] = EP_TYPE_INTERRUPT_IN;

src/HID/HID.h

@@ -141,20 +141,19 @@ class HID_ : public PluggableUSBModule
 private:
     uint8_t epType[2];
 
-    HIDSubDescriptor* rootNode;
+    HIDSubDescriptor* rootNode = nullptr;
     uint16_t descriptorSize;
 
     uint8_t protocol;
     uint8_t idle;
 
     // Buffer pointer to hold the feature data
-    HIDReport* rootReport;
+    HIDReport* rootReport = nullptr;
     uint16_t reportCount;
 
-    Serial_ *dbg;
-
-    const char *serial;
+    Serial_ *dbg = nullptr;
 
+    const char *serial = nullptr; 
 };
 
 // Replacement for global singleton.