enable echo warning whe nget default value

Author: xieguigang

R/context/set_config.R

@@ -38,7 +38,7 @@ const set_config = function(configs = list()) {
 #'    a type cast function expression invoke example as: 
 #'    ``as.logical``, ``as.double``, etc maybe required.
 #' 
-const get_config = function(name, default = NULL) {
+const get_config = function(name, default = NULL, warn_msg = NULL) {
     const path    = strsplit(name, "$", fixed = TRUE);
     const verbose = as.logical(getOption("verbose"));
 
@@ -60,7 +60,16 @@ const get_config = function(name, default = NULL) {
         }
     }
 
-    return(config || default);
+    if (is.null(warn_msg)) {
+        return(config || default);
+    } else {
+        if (is.null(config)) {
+            echo_warning(warn_msg);
+            default;
+        } else {
+            config;
+        }
+    }    
 }
 
 #' pull all configuration value from workflow registry