added assignment from value, conversion to database_type and appropriate tests

source/core/utils/errors.cpp

@@ -10,6 +10,8 @@ std::string utils_category_impl::message(const int ev) const {
   switch (static_cast<utils_error>(ev)) {
     case (utils_error::InvalidVersionString):
       return "Invalid version string";
+    case utils_error::IdentifierTypeMismatch:
+      return "Identifier type mismatch";
     default:
       return "Unknown error";
   }