Fix for CONPY-191:

When connected to a database server which doesn't support bulk
execution, we need to set bind.is_null instead of changing the buffer
type to MYSQL_TYPE_NULL. This will keep the original buffer type.

include/mariadb_python.h

@@ -236,6 +236,7 @@ typedef struct {
     void *buffer;
     unsigned char num[8];
     MYSQL_TIME tm;
+    uint8_t is_null;
 } MrdbParamValue;
 
 typedef struct {

mariadb/mariadb_codecs.c

@@ -1298,11 +1298,12 @@ mariadb_param_to_bind(MrdbCursor *self,
         bind->u.indicator[0]= value->indicator;
         goto end;
     }
-
-    if (!value->value)
+    value->is_null= value->value == NULL;
+    if (value->is_null)
     {
-      bind->buffer_type= MYSQL_TYPE_NULL;
+      bind->is_null= (my_bool *)&value->is_null;
     } else {
+      bind->is_null= NULL;
       if (IS_NUM(bind->buffer_type))
       {
           bind->buffer= value->num;
@@ -1313,7 +1314,6 @@ mariadb_param_to_bind(MrdbCursor *self,
           if (_PyLong_Sign(value->value) < 0)
               is_negative= 1;
       }
-    }
 
       switch(bind->buffer_type)
       {
@@ -1412,6 +1412,7 @@ mariadb_param_to_bind(MrdbCursor *self,
           default:
               rc= 1;
       }
+    }
 end:
     MARIADB_BLOCK_THREADS(self);
     return rc;

testing/test/integration/test_cursor.py

@@ -1163,6 +1163,20 @@ class TestCursor(unittest.TestCase):
         del cursor
         connection.close()
 
+    def test_conpy191(self):
+        connection= create_connection()
+        cursor= connection.cursor()
+        cursor.execute("create temporary table t1 (a int, b int, c int)")
+        data= [(None,1,1),(2,None,2),(3,3,None)]
+
+        cursor.executemany("INSERT INTO t1 VALUES (?,?,?)", data);
+
+        cursor.execute("SELECT a,b,c FROM t1")
+        result= cursor.fetchall()
+        self.assertEqual(data, result)
+        del cursor
+        connection.close()
+
     def test_conpy91(self):
         with create_connection() as connection:
             with connection.cursor() as cursor: