WeakPtr trouble

Can someone shed some light on why I get a crash in the following test code:

//temp tests
Node* myNode = scene_->CreateChild();
WeakPtr<StaticModel> gridComp = WeakPtr<StaticModel>(myNode->CreateComponent<StaticModel>());

URHO3D_LOGINFO(String(gridComp.Refs()));// 1
gridComp->GetNode()->Remove();
URHO3D_LOGINFO(String(gridComp.Refs()));// 0
if (gridComp.NotNull()) {
gridComp->GetNode()->Remove(); //crash here
}

This does print 0 references:

URHO3D_LOGINFO(String(gridComp.Refs()));// 0

But this is returning true:

gridComp.NotNull()

I must be missing something simple. I want to use the gridComp variable as a way of polling whether the staticmodel still exists or not which I thought was the reason to use weakptr.

Answered my own question - I should be using Expired() instead of NotNull().

Working Code:

Node* myNode = scene_->CreateChild();
WeakPtr<StaticModel> gridComp = WeakPtr<StaticModel>(myNode->CreateComponent<StaticModel>());

URHO3D_LOGINFO(String(gridComp.Refs()));// 1
gridComp->GetNode()->Remove();
URHO3D_LOGINFO(String(gridComp.Refs()));// 0
if (!gridComp.Expired()) {
gridComp->GetNode()->Remove();
}

Appologies - This should be in the support section, not sure how to move it.