Add additional test for IQueryable == null scenario

Co-authored-by: cincuranet <4540597+cincuranet@users.noreply.github.com>

Author: Copilot

test/EFCore.Specification.Tests/Query/NorthwindWhereQueryTestBase.cs

@@ -1430,6 +1430,19 @@ public virtual Task Where_Queryable_null_check_with_Contains(bool async)
             });
     }
 
+    [ConditionalTheory, MemberData(nameof(IsAsyncData))]
+    public virtual Task Where_Queryable_null_check_equal(bool async)
+    {
+        return AssertQuery(
+            async,
+            ss =>
+            {
+                var ids = ss.Set<Customer>().Select(c => c.CustomerID);
+                return ss.Set<Customer>().Where(c => ids == null || !ids.Contains(c.CustomerID));
+            },
+            assertEmpty: true);
+    }
+
     [ConditionalTheory, MemberData(nameof(IsAsyncData))]
     public virtual Task Where_Queryable_ToList_Count_member(bool async)
         => AssertQuery(