added VB unit tests and fixed a bug in predicate translator.

Author: craiggwilson

Driver/Linq/Translators/PredicateTranslator.cs

@@ -460,7 +460,7 @@ private IMongoQuery BuildContainsKeyQuery(MethodCallExpression methodCallExpress
         private IMongoQuery BuildContainsQuery(MethodCallExpression methodCallExpression)
         {
             // handle IDictionary Contains the same way as IDictionary<TKey, TValue> ContainsKey
-            if (typeof(IDictionary).IsAssignableFrom(methodCallExpression.Object.Type))
+            if (methodCallExpression.Object != null && typeof(IDictionary).IsAssignableFrom(methodCallExpression.Object.Type))
             {
                 return BuildContainsKeyQuery(methodCallExpression);
             }

DriverUnitTestsVB/DriverUnitTestsVB.vbproj

@@ -69,6 +69,7 @@
   <ItemGroup>
     <Compile Include="Linq\MongoQueryableTests.vb" />
     <Compile Include="Linq\MongoQueryProviderTests.vb" />
+    <Compile Include="Linq\SelectDictionaryTests.vb" />
     <Compile Include="Linq\SelectNullableTests.vb" />
     <Compile Include="Linq\SelectOfTypeHierarchicalTests.vb" />
     <Compile Include="Linq\SelectOfTypeTests.vb" />