Elastix should stop running (and fail) when initial transform is not supported

[N-Dekker]

When an initial transform is not supported, elastix produces an error message as log output, saying something like:

Error:
Transform(index 1) - This component is not installed!

However, it does not stop running the registration. Shouldn't it?

The error message comes from ComponentDatabase::GetCreator at:

elastix/Core/Install/elxComponentDatabase.cxx

Lines 108 to 109 in 115d8e1

	log::error(std::ostringstream{} << "Error: \n" << name << "(index " << i << ") - This component is not installed!");
	return nullptr;

But it then just returns nullptr, which is handled by TransformBase::ReadInitialTransformFromConfiguration to just do nothing:

elastix/Core/ComponentBaseClasses/elxTransformBase.hxx

Lines 485 to 492 in 115d8e1

	const PtrToCreator testcreator =
	ElastixMain::GetComponentDatabase().GetCreator(initialTransformName, this->m_Elastix->GetDBIndex());
	const itk::Object::Pointer initialTransform = (testcreator == nullptr) ? nullptr : testcreator();
	const auto elx_initialTransform = dynamic_cast<Self *>(initialTransform.GetPointer());
	/** Call the ReadFromFile method of the initialTransform. */
	if (elx_initialTransform != nullptr)

---

For the record, back in 2004 (e.g., revision ab62f3d) , TransformBase already handled a failure of ComponentDatabase::GetCreator by just doing nothing:

elastix/src/Core/ComponentBaseClasses/elxTransformBase.hxx

Lines 342 to 349 in ab62f3d

	testcreator = this->GetElastix()->GetComponentDatabase()->
	GetCreator( InitialTransformName, m_Elastix->GetDBIndex() );
	initialTransform = testcreator ? testcreator() : NULL;
	Self * elx_initialTransform = dynamic_cast< Self * >( initialTransform.GetPointer() );
	/** Call the ReadFromFile method of the initialTransform. */
	if ( elx_initialTransform )