Rlua conversion error

`thread 'arbiter:5037cb99-0989-4fb1-b855-945ba10943dc:actor' panicked at 'Lua error: FromLuaConversionError { from: "nil", to: "String", message: Some("expected string or number") }', .../.cargo/registry/src/github.com-1ecc6299db9ec823/actix-lua-0.5.1/src/message.rs:123:17
`

This is happening everywhere, when an rlua function expects a string or some other type and another type is given, it straight up panics the thread and doesn't let either lua nor the calling rust code recover from the error. This is the cause for #88.

Seems like it's an actix-lua issue, or maybe even rlua but I doubt it.