Index: src/alter.c
==================================================================
--- src/alter.c
+++ src/alter.c
@@ -903,11 +903,11 @@
   /* Set zQuot to point to a buffer containing a quoted copy of the 
   ** identifier zNew. If the corresponding identifier in the original 
   ** ALTER TABLE statement was quoted (bQuote==1), then set zNew to
   ** point to zQuot so that all substitutions are made using the
   ** quoted version of the new column name.  */
-  zQuot = sqlite3_mprintf("\"%w\"", zNew);
+  zQuot = sqlite3MPrintf(db, "\"%w\"", zNew);
   if( zQuot==0 ){
     return SQLITE_NOMEM;
   }else{
     nQuot = sqlite3Strlen30(zQuot);
   }
@@ -1100,25 +1100,21 @@
   sqlite3_value **argv
 ){
   sqlite3 *db = sqlite3_context_db_handle(context);
   RenameCtx sCtx;
   const char *zSql = (const char*)sqlite3_value_text(argv[0]);
-  int nSql = sqlite3_value_bytes(argv[0]);
   const char *zDb = (const char*)sqlite3_value_text(argv[3]);
   const char *zTable = (const char*)sqlite3_value_text(argv[4]);
   int iCol = sqlite3_value_int(argv[5]);
   const char *zNew = (const char*)sqlite3_value_text(argv[6]);
-  int nNew = sqlite3_value_bytes(argv[6]);
   int bQuote = sqlite3_value_int(argv[7]);
   const char *zOld;
   int bTemp = 0;
   int rc;
-  char *zErr = 0;
   Parse sParse;
   Walker sWalker;
   Index *pIdx;
-  char *zOut = 0;
   int i;
   Table *pTab;
 #ifndef SQLITE_OMIT_AUTHORIZATION
   sqlite3_xauth xAuth = db->xAuth;
 #endif
@@ -1419,10 +1415,12 @@
 ){
   sqlite3 *db = sqlite3_context_db_handle(context);
   unsigned char const *zDb = sqlite3_value_text(argv[0]);
   unsigned char const *zInput = sqlite3_value_text(argv[1]);
   int bTemp = sqlite3_value_int(argv[4]);
+
+  if( zInput==0 ) return;
 
 #ifndef SQLITE_OMIT_AUTHORIZATION
   sqlite3_xauth xAuth = db->xAuth;
   db->xAuth = 0;
 #endif