'System.Nullable' does not satisfy the 'Structure' constraint for type parameter '<typeparametername>'
A generic type is invoked passing a type argument ofto a type parameter with a Structure constraint.
The common language runtime (CLR) specifically disallows the Nullable structure as a type argument to itself. Even though it is a structure and would otherwise satisfy a Structure constraint, using it recursively could lead to awkward constructions such as Nullable(Of Nullable(Of Nullable)).
Error ID: BC32115
To correct this error
Either remove the Structure constraint from the type parameter, or change the type argument to some value type other than Nullable.