Don't error() upon access of non-existent fields

One thing I've that annoyed me in the past, that bit me today as well, is that lgi raises errors upon reads for non-existent fields instead of returning nil. I find this annoying since it's (to me) very different from the standard Lua way of just returning nil. Is there a rationale for doing it this way?

My use case btw is a method that accepts either lgi objects or other objects that can be converted to lgi objects for a special conversion method. Whereas this would be a standard Lua conditional one-liner it now requires pcall.

Start by reproducing the reported access to a non-existent field on an lgi object and compare it with standard Lua behavior. The work is done when such reads return nil without requiring pcall, while the behavior for existing fields remains correct; the issue does not name a file or test to begin with.