Allow the complex value to be defined as an empty string.

This makes conversion from strings to complex values possible
without the loss of functionality.

src/http/modules/ngx_http_auth_basic_module.c

@@ -117,7 +117,7 @@ ngx_http_auth_basic_handler(ngx_http_request_t *r)
 
     alcf = ngx_http_get_module_loc_conf(r, ngx_http_auth_basic_module);
 
-    if (alcf->realm.len == 0 || alcf->user_file.value.len == 0) {
+    if (alcf->realm.len == 0 || alcf->user_file.value.data == NULL) {
         return NGX_DECLINED;
     }
 
@@ -390,7 +390,7 @@ ngx_http_auth_basic_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
         conf->realm = prev->realm;
     }
 
-    if (conf->user_file.value.len == 0) {
+    if (conf->user_file.value.data == NULL) {
         conf->user_file = prev->user_file;
     }
 
@@ -456,7 +456,7 @@ ngx_http_auth_basic_user_file(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
     ngx_str_t                         *value;
     ngx_http_compile_complex_value_t   ccv;
 
-    if (alcf->user_file.value.len) {
+    if (alcf->user_file.value.data) {
         return "is duplicate";
     }
 

src/http/modules/ngx_http_fastcgi_module.c

@@ -3014,7 +3014,7 @@ ngx_http_fastcgi_cache_key(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 
     value = cf->args->elts;
 
-    if (flcf->cache_key.value.len) {
+    if (flcf->cache_key.value.data) {
         return "is duplicate";
     }
 

src/http/modules/ngx_http_proxy_module.c

@@ -837,7 +837,7 @@ ngx_http_proxy_create_key(ngx_http_request_t *r)
         return NGX_ERROR;
     }
 
-    if (plcf->cache_key.value.len) {
+    if (plcf->cache_key.value.data) {
 
         if (ngx_http_complex_value(r, &plcf->cache_key, key) != NGX_OK) {
             return NGX_ERROR;
@@ -3651,7 +3651,7 @@ ngx_http_proxy_cache_key(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 
     value = cf->args->elts;
 
-    if (plcf->cache_key.value.len) {
+    if (plcf->cache_key.value.data) {
         return "is duplicate";
     }
 

src/http/modules/ngx_http_scgi_module.c

@@ -1771,7 +1771,7 @@ ngx_http_scgi_cache_key(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 
     value = cf->args->elts;
 
-    if (scf->cache_key.value.len) {
+    if (scf->cache_key.value.data) {
         return "is duplicate";
     }
 

src/http/modules/ngx_http_sub_filter_module.c

@@ -628,7 +628,7 @@ ngx_http_sub_filter(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
     ngx_str_t                         *value;
     ngx_http_compile_complex_value_t   ccv;
 
-    if (slcf->match.len) {
+    if (slcf->match.data) {
         return "is duplicate";
     }
 
@@ -688,7 +688,7 @@ ngx_http_sub_merge_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_value(conf->once, prev->once, 1);
     ngx_conf_merge_str_value(conf->match, prev->match, "");
 
-    if (conf->value.value.len == 0) {
+    if (conf->value.value.data == NULL) {
         conf->value = prev->value;
     }
 

src/http/modules/ngx_http_uwsgi_module.c

@@ -1807,7 +1807,7 @@ ngx_http_uwsgi_cache_key(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 
     value = cf->args->elts;
 
-    if (uwcf->cache_key.value.len) {
+    if (uwcf->cache_key.value.data) {
         return "is duplicate";
     }
 

src/http/ngx_http_core_module.c

@@ -4593,7 +4593,7 @@ ngx_http_core_error_page(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 
     ngx_str_null(&args);
 
-    if (cv.lengths == NULL && uri.data[0] == '/') {
+    if (cv.lengths == NULL && uri.len && uri.data[0] == '/') {
         p = (u_char *) ngx_strchr(uri.data, '?');
 
         if (p) {

src/http/ngx_http_script.c

@@ -114,11 +114,6 @@ ngx_http_compile_complex_value(ngx_http_compile_complex_value_t *ccv)
 
     v = ccv->value;
 
-    if (v->len == 0) {
-        ngx_conf_log_error(NGX_LOG_EMERG, ccv->cf, 0, "empty parameter");
-        return NGX_ERROR;
-    }
-
     nv = 0;
     nc = 0;
 
@@ -133,8 +128,9 @@ ngx_http_compile_complex_value(ngx_http_compile_complex_value_t *ccv)
         }
     }
 
-    if (v->data[0] != '$' && (ccv->conf_prefix || ccv->root_prefix)) {
-
+    if ((v->len == 0 || v->data[0] != '$')
+        && (ccv->conf_prefix || ccv->root_prefix))
+    {
         if (ngx_conf_full_name(ccv->cf->cycle, v, ccv->conf_prefix) != NGX_OK) {
             return NGX_ERROR;
         }