Base: Add isNullOrEmpty string helper

This adds isNullOrEmpty string helper that cheks if string is... well
null or empty. It is done to improve readability of the code and better
express intent.

src/Base/Tools.h

@@ -301,6 +301,11 @@ struct BaseExport Tools
      */
     static std::string quoted(const std::string&);
 
+    static constexpr bool isNullOrEmpty(const char* str)
+    {
+        return !str || str[0] == '\0';
+    }
+
     /**
      * @brief joinList
      * Join the vector of strings \a vec using the separator \a sep