When method parameter has default value it is ignored by Zend\Di and it passes {{NULL}} if parameter is not defined explicitly. As an example try creating {{Zend\Authentication\Storage\Session}} without any parameters defined in Di configuration - it's constructor allows to create instance without passing any parameter and assigns default values then. But Di sees no parameter values in configuration and passes {{NULL}}, which overrides default values.

I think Di should check if parameter is specified explicitly to {{NULL}} in instance manager configuration and if not, do not pass anything (even NULL).

Problem lies in library/Zend/Di/Di.php at line 616 (commit 9bd4f0a30b1ab6b0d3ab2263b987a35bcab30393):

{{$resolvedParams[$index] = null;}} should assign default parameter vlaue if not explicitly specified by Di definition.