nginx-0.0.1-2003-11-18-19:49:00 import
diff --git a/src/http/ngx_http_busy_lock.c b/src/http/ngx_http_busy_lock.c
index 085cd56..172e15e 100644
--- a/src/http/ngx_http_busy_lock.c
+++ b/src/http/ngx_http_busy_lock.c
@@ -103,6 +103,10 @@
 void ngx_http_busy_unlock(ngx_http_busy_lock_t *bl,
                           ngx_http_busy_lock_ctx_t *bc)
 {
+    if (bl == NULL) {
+        return;
+    }
+
     if (bl->md5) {
         bl->md5_mask[bc->slot / 8] &= ~(1 << (bc->slot & 7));
         bl->cachable--;