As Sascha, Jan, Stefan and I discussed in the last bug-squashing, change the interface of all mitk::Equal methods to:

bool mitk::Equal(const mitk::DataType& i1, const mitk::DataType&)

in order to avoid NULL inputs. Also declare the old interface deprecated e.g.:
DEPRECATED(bool mitk::Equal(const mitk::Image* i1, const mitk::Image*)).

This affects the following core header files:
mitkImage
mitkGeometry3D
mitkVector
mitkPointSet
mitkSurface

Corresponding EqualTests will be adapted.