Feature #1069

- Throw a custom error if uda.<uda-name>.type is not set
  but, for example, uda.<uda-name>.label is set.

src/columns/Column.cpp

@@ -183,6 +183,8 @@ Column* Column::uda (const std::string& name)
 
   std::string key = "uda." + name + ".type";
   c->_type = context.config.get (key);
+  if (c->_type == "")
+    throw format (STRING_UDA_TYPE_MISSING, name);
   if (c->_type != "string"   &&
       c->_type != "date"     &&
       c->_type != "duration" &&