Merge pull request #12048 from kjbracey-arm/sharedptr_nullptr

SharedPtr: add nullptr constructor

Author: adbridge

TESTS/mbed_platform/SharedPtr/main.cpp

@@ -65,7 +65,7 @@ void test_single_sharedptr_lifetime()
  */
 void test_instance_sharing()
 {
-    SharedPtr<TestStruct> s_ptr1(NULL);
+    SharedPtr<TestStruct> s_ptr1(nullptr);
 
     // Sanity-check value of counter
     TEST_ASSERT_EQUAL(0, TestStruct::s_count);
@@ -80,7 +80,7 @@ void test_instance_sharing()
 
     TEST_ASSERT_EQUAL(1, TestStruct::s_count);
 
-    s_ptr1 = NULL;
+    s_ptr1 = nullptr;
 
     // Destroy shared pointer
     TEST_ASSERT_EQUAL(0, TestStruct::s_count);

platform/SharedPtr.h

@@ -75,6 +75,13 @@ class SharedPtr {
     {
     }
 
+    /**
+     * @brief Create empty SharedPtr not pointing to anything.
+     */
+    constexpr SharedPtr(std::nullptr_t) : SharedPtr()
+    {
+    }
+
     /**
      * @brief Create new SharedPtr
      * @param ptr Pointer to take control over