Something

Index: domain.c
===================================================================
--- domain.c    (revision 53280)
+++ domain.c    (working copy)
@@ -758,12 +758,14 @@
                mono_defaults.corlib, "System.Threading", "ExecutionContext");

        /*
-        * Note that mono_defaults.generic_array_class is only non-NULL if we're
+        * Note that mono_defaults.generic_*_class is only non-NULL if we're
         * using the 2.0 corlib.
         */
        mono_class_init (mono_defaults.array_class);
        mono_defaults.generic_array_class = mono_class_from_name (
                mono_defaults.corlib, "System", "Array/InternalArray`1");
+       mono_defaults.generic_nullable_class = mono_class_from_name (
+               mono_defaults.corlib, "System", "Nullable`1");

        domain->friendly_name = g_path_get_basename (filename);

Index: class-internals.h
===================================================================
--- class-internals.h   (revision 53280)
+++ class-internals.h   (working copy)
@@ -680,6 +680,7 @@
        MonoClass *runtimesecurityframe_class;
        MonoClass *executioncontext_class;
        MonoClass *generic_array_class;
+       MonoClass *generic_nullable_class;
 } MonoDefaults;