Add get_first_non_empty and use it into Database to simplify a little bit

src/utils/get_first_non_empty.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <string>
+
+bool is_empty(const std::string& val);
+bool is_empty(const int& val);
+
+template <typename T>
+T get_first_non_empty(T&& last)
+{
+  return last;
+}
+
+template <typename T, typename... Args>
+T get_first_non_empty(T&& first, Args&&... args)
+{
+  if (!is_empty(first))
+    return first;
+  return get_first_non_empty(std::forward<Args>(args)...);
+}