DataAadatpor API has no way to indicate method failed

If the following methods fail there is no reliable way to let the caller know that his call has failed. Note that in the case of GetMesh it is valid to return a nullptr, for instance if the analysis is run on more cores than the simulation than some number of processes will return nullptr.

virtual vtkDataObject* GetMesh(bool structure_only=false) = 0;
virtual std::string GetArrayName(int association, unsigned int index) = 0;

How is the best way to indicate an error for this call? Could an adaptor not provide arrays? in that case 0 would not be an error. A negative return could indicate an error if the return type was signed.

virtual unsigned int GetNumberOfArrays(int association) = 0;