Nil config items cause execeptions by not causing use of default values

[ddoherty03]

Description

When I set certain options, Readline would set them to default values, but not Reline:

::Readline.input = nil  # Should set input to $stdin
::Readline.output = nil  # Should set output to $stdout
::Readline.special_prefixes = nil  # Should set to empty string ''

What are your expected behavior and actual behavior of your environment?

In Reline, these seem to keep and use the nil value, raising errors. I would expect it to behave the same as Readline if it aspires to be a drop-in replacement for it.

The above are those I've stumbled across. Should see that all config options get the Readline default when set to nil.

Terminal Emulator

What's your terminal emulator?

KDE's konsole, but this is independent of the emulator.