UpdateGlue: never pass null to update_enqueue()

src/Main.cxx

@@ -468,7 +468,7 @@ int mpd_main(int argc, char *argv[])
 	if (create_db) {
 		/* the database failed to load: recreate the
 		   database */
-		unsigned job = update_enqueue(nullptr, true);
+		unsigned job = update_enqueue("", true);
 		if (job == 0)
 			FatalError("directory update failed");
 	}

src/OtherCommands.cxx

@@ -157,7 +157,7 @@ handle_lsinfo(Client *client, int argc, char *argv[])
 enum command_return
 handle_update(Client *client, gcc_unused int argc, char *argv[])
 {
-	const char *path = NULL;
+	const char *path = "";
 	unsigned ret;
 
 	assert(argc <= 2);
@@ -166,7 +166,7 @@ handle_update(Client *client, gcc_unused int argc, char *argv[])
 
 		if (*path == 0 || strcmp(path, "/") == 0)
 			/* backwards compatibility with MPD 0.15 */
-			path = NULL;
+			path = "";
 		else if (!uri_safe_local(path)) {
 			command_error(client, ACK_ERROR_ARG,
 				      "Malformed path");
@@ -188,7 +188,7 @@ handle_update(Client *client, gcc_unused int argc, char *argv[])
 enum command_return
 handle_rescan(Client *client, gcc_unused int argc, char *argv[])
 {
-	const char *path = NULL;
+	const char *path = "";
 	unsigned ret;
 
 	assert(argc <= 2);

src/UpdateGlue.hxx

@@ -20,6 +20,8 @@
 #ifndef MPD_UPDATE_GLUE_HXX
 #define MPD_UPDATE_GLUE_HXX
 
+#include "Compiler.h"
+
 void update_global_init(void);
 
 void update_global_finish(void);
@@ -30,10 +32,11 @@ isUpdatingDB(void);
 /**
  * Add this path to the database update queue.
  *
- * @param path a path to update; if NULL or an empty string,
+ * @param path a path to update; if an empty string,
  * the whole music directory is updated
  * @return the job id, or 0 on error
  */
+gcc_nonnull_all
 unsigned
 update_enqueue(const char *path, bool discard);