Crash on null arguments

[MarSoft]

Hello. I use MariaDB 10.0.20. I installed this great plugin. It works fine, but if any of input parameters is NULL, my MariaDB server restarts and I get «ERROR 2013 (HY000): Lost connection to MySQL server during query» error.
For now I added a workaround with additional «WHERE lat IS NOT NULL AND lon IS NOT NULL and ...» for all lat&lons. But I think it would be great to add such checking to the function itself.

[MarSoft]

Or probably make it return NULL if any of arguments is NULL, like built-in GLength function does.