change ngx_conf_merge_ptr_value() and update fastcgi_catch_stderr

src/core/ngx_conf_file.h

diff --git a/src/core/ngx_conf_file.h b/src/core/ngx_conf_file.h
index 2e91d0b..c3e3e9a 100644
--- a/src/core/ngx_conf_file.h
+++ b/src/core/ngx_conf_file.h
@@ -257,8 +257,8 @@
     }
 
 #define ngx_conf_merge_ptr_value(conf, prev, default)                        \
-    if (conf == NULL) {                                                      \
-        conf = (prev == NULL) ? default : prev;                              \
+    if (conf == NGX_CONF_UNSET_PTR) {                                        \
+        conf = (prev == NGX_CONF_UNSET_PTR) ? default : prev;                \
     }
 
 #define ngx_conf_merge_uint_value(conf, prev, default)                       \

src/http/modules/ngx_http_fastcgi_module.c

diff --git a/src/http/modules/ngx_http_fastcgi_module.c b/src/http/modules/ngx_http_fastcgi_module.c
index c1ce79c..ac14d75 100644
--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -1640,7 +1640,6 @@
      *     conf->upstream.hide_headers_hash = { NULL, 0 };
      *     conf->upstream.hide_headers = NULL;
      *     conf->upstream.pass_headers = NULL;
-     *     conf->upstream.catch_stderr = NULL;
      *     conf->upstream.schema = { 0, NULL };
      *     conf->upstream.uri = { 0, NULL };
      *     conf->upstream.location = NULL;
@@ -1675,6 +1674,8 @@
     /* "fastcgi_cyclic_temp_file" is disabled */
     conf->upstream.cyclic_temp_file = 0;
 
+    conf->catch_stderr = NGX_CONF_UNSET_PTR;
+
     return conf;
 }