Fix build warnings

It looks like once you start using the FOLLY_NULLABLE or FOLLY_NONNULL macros in
a class, it's all or nothing or you get build warnings. This change addresses
that based on the assumptions of the underlying code.

folly/logging/LoggerDB.h

@@ -57,7 +57,7 @@ class LoggerDB {
    * This creates the LogCategory for the specified name if it does not exist
    * already.
    */
-  LogCategory* getCategory(folly::StringPiece name);
+  LogCategory* FOLLY_NONNULL getCategory(folly::StringPiece name);
 
   /**
    * Get the LogCategory for the specified name, if it already exists.
@@ -80,7 +80,10 @@ class LoggerDB {
    * use a less verbose level than its parent categories.)
    */
   void setLevel(folly::StringPiece name, LogLevel level, bool inherit = true);
-  void setLevel(LogCategory* category, LogLevel level, bool inherit = true);
+  void setLevel(
+      LogCategory* FOLLY_NONNULL category,
+      LogLevel level,
+      bool inherit = true);
 
   /**
    * Get a LogConfig object describing the current state of the LoggerDB.
@@ -170,12 +173,12 @@ class LoggerDB {
    */
   LogLevel xlogInit(
       folly::StringPiece categoryName,
-      std::atomic<LogLevel>* xlogCategoryLevel,
-      LogCategory** xlogCategory);
-  LogCategory* xlogInitCategory(
+      std::atomic<LogLevel>* FOLLY_NONNULL xlogCategoryLevel,
+      LogCategory* FOLLY_NULLABLE * FOLLY_NULLABLE xlogCategory);
+  LogCategory* FOLLY_NONNULL xlogInitCategory(
       folly::StringPiece categoryName,
-      LogCategory** xlogCategory,
-      std::atomic<bool>* isInitialized);
+      LogCategory* FOLLY_NONNULL * FOLLY_NONNULL xlogCategory,
+      std::atomic<bool>* FOLLY_NONNULL isInitialized);
 
   enum TestConstructorArg { TESTING };
 
@@ -240,7 +243,8 @@ class LoggerDB {
    * Windows, and prints the message to stderr on other platforms.  It also
    * rate limits messages if they are arriving too quickly.
    */
-  static void setInternalWarningHandler(InternalWarningHandler handler);
+  static void setInternalWarningHandler(
+      InternalWarningHandler FOLLY_NULLABLE handler);
 
  private:
   using LoggerNameMap = std::unordered_map<
@@ -274,12 +278,12 @@ class LoggerDB {
   LoggerDB& operator=(LoggerDB const&) = delete;
 
   LoggerDB();
-  LogCategory* getOrCreateCategoryLocked(
+  LogCategory* FOLLY_NONNULL getOrCreateCategoryLocked(
       LoggerNameMap& loggersByName, folly::StringPiece name);
-  LogCategory* createCategoryLocked(
+  LogCategory* FOLLY_NONNULL createCategoryLocked(
       LoggerNameMap& loggersByName,
       folly::StringPiece name,
-      LogCategory* parent);
+      LogCategory* FOLLY_NONNULL parent);
 
   using NewHandlerMap =
       std::unordered_map<std::string, std::shared_ptr<LogHandler>>;
@@ -289,12 +293,12 @@ class LoggerDB {
   void startConfigUpdate(
       const Synchronized<HandlerInfo>::LockedPtr& handlerInfo,
       const LogConfig& config,
-      NewHandlerMap* handlers,
-      OldToNewHandlerMap* oldToNewHandlerMap);
+      NewHandlerMap* FOLLY_NONNULL handlers,
+      OldToNewHandlerMap* FOLLY_NONNULL oldToNewHandlerMap);
   void finishConfigUpdate(
       const Synchronized<HandlerInfo>::LockedPtr& handlerInfo,
-      NewHandlerMap* handlers,
-      OldToNewHandlerMap* oldToNewHandlerMap);
+      NewHandlerMap* FOLLY_NONNULL handlers,
+      OldToNewHandlerMap* FOLLY_NONNULL oldToNewHandlerMap);
   std::vector<std::shared_ptr<LogHandler>> buildCategoryHandlerList(
       const NewHandlerMap& handlerMap,
       StringPiece categoryName,