Style: use ngx_str_null().

src/core/ngx_resolver.c

diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c
index 645738c..42acc83 100644
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -2722,8 +2722,7 @@
     }
 
     if (len == -1) {
-        name->len = 0;
-        name->data = NULL;
+        ngx_str_null(name);
         return NGX_OK;
     }