use NULL instead of 0

src/http/modules/ngx_http_proxy_module.c

diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index caf27b6..e311bb9 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -572,7 +572,7 @@
 
     u = r->upstream;
 
-    if (plcf->proxy_lengths == 0) {
+    if (plcf->proxy_lengths == NULL) {
         ctx->vars = plcf->vars;
         u->schema = plcf->vars.schema;
 #if (NGX_HTTP_SSL)