Problem when DistinguishedName is Empty

[georg-x]

Get-ADObject $CA.DistinguishedName gives Null value:

Get-ADObject : Cannot validate argument on parameter 'Identity'. The argument is null. Provide a valid value for the
argument, and then try running the command again.
At line:1 char:33
+ $CATemplateNames = Get-ADObject $CA.DistinguishedName -Properties ce ...
+                                 ~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidData: (:) [Get-ADObject], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.ActiveDirectory.Management.Commands.GetADObje
   ct