Fix folly::dynamic ordering comparison operator bug for Type::NULLT vs Type::NULLT

Summary:
Fixes the bug referenced in the base commit of this stack.

Given that `folly::dynamic(nullptr) == folly::dynamic(nullptr)` returns true, `folly::dynamic(nullptr) < folly::dynamic(nullptr)` should return false to maintain ordering properties.

Reviewed By: Gownta

Differential Revision: D33456202

fbshipit-source-id: 3fc994cd76d6e119884e017f68b445ed438f7cea

folly/dynamic-inl.h

@@ -567,7 +567,7 @@ struct dynamic::CompareOp<dynamic::ObjectImpl> {
 template <>
 struct dynamic::CompareOp<std::nullptr_t> {
   static bool comp(std::nullptr_t const&, std::nullptr_t const&) {
-    return true;
+    return false;
   }
 };
 

folly/test/DynamicTest.cpp

@@ -540,14 +540,7 @@ void testComparisonOperatorsForEqualDynamicValues(
     const dynamic& valueA, const dynamic& valueB) {
   testEqualityOperatorsForEqualValues(valueA, valueB);
 
-  if (valueA.isNull() && valueB.isNull()) {
-    // There's a bug in null vs null ordering comparison. This test is mainly
-    // for highlighting the behavior which will be fixed in a subsequent commit.
-    EXPECT_TRUE(valueA < valueB);
-    EXPECT_TRUE(valueA > valueB);
-    EXPECT_FALSE(valueB <= valueA);
-    EXPECT_FALSE(valueB >= valueA);
-  } else if (valueA.isObject() || valueB.isObject()) {
+  if (valueA.isObject() || valueB.isObject()) {
     // Objects don't support ordering
     testOrderingOperatorsThrowForObjectTypes(valueA, valueB);
   } else {