set crow static directory and template directory in case of an empty …

…static_dir or template dir parameter to blueprints url prefix as default.

added also error log output in case of a top level blueprint with empty static_dir (should not happen anymore due to above fix, but at least not silently ignored)

include/crow/app.h

@@ -456,8 +456,10 @@ namespace crow
 
             for (Blueprint* bp : router_.blueprints())
             {
-                if (bp->static_dir().empty()) continue;
-
+                if (bp->static_dir().empty()) {
+                    CROW_LOG_ERROR << "Blueprint " << bp->prefix() << " and its sub-blueprints ignored due to empty static directory.";
+                    continue;
+                }
                 auto static_dir_ = crow::utility::normalize_path(bp->static_dir());
 
                 bp->new_rule_tagged<crow::black_magic::get_parameter_tag(CROW_STATIC_ENDPOINT)>(CROW_STATIC_ENDPOINT)([static_dir_](crow::response& res, std::string file_path_partial) {

include/crow/routing.h

@@ -1095,16 +1095,19 @@ namespace crow // NOTE: Already documented in "crow/app.h"
         Node head_;
     };
 
-    /// A blueprint can be considered a smaller section of a Crow app, specifically where the router is conecerned.
+    /// A blueprint can be considered a smaller section of a Crow app, specifically where the router is concerned.
 
     ///
     /// You can use blueprints to assign a common prefix to rules' prefix, set custom static and template folders, and set a custom catchall route.
     /// You can also assign nest blueprints for maximum Compartmentalization.
     class Blueprint
     {
     public:
-        Blueprint(const std::string& prefix):
-          prefix_(prefix){};
+        Blueprint(const std::string& prefix)
+          : prefix_(prefix),
+            static_dir_(prefix),
+            templates_dir_(prefix)
+            {};
 
         Blueprint(const std::string& prefix, const std::string& static_dir):
           prefix_(prefix), static_dir_(static_dir){};