weird issue with the proxy settings if 'proxy_server' seems to be set not fully correct

We use archive module in our setup and we found a weird issue: puppet was failing with the error
Error: Failed to apply catalog: undefined method `to_sym' for nil:NilClass
in the following line

puppet-archive/lib/puppet/type/archive.rb

Line 278 in 7c9734e

self[:proxy_type] ||= URI(self[:proxy_server]).scheme.to_sym

That looked weird. On some our servers we have proxy but on other ones we don't, there proxy_server was set to undef, but, as I understand, Ruby considered that it's not empty and tried to use URI.scheme (which returned "nil" and then failed)

I tried different approaches and had to hack the code to make it working, checking not self[:proxy_server] in Line 277 but URI(self[:proxy_server]).scheme

Can you please have a look into this issue? I am not familiar with Ruby and that was the easiest approach I could find.
Maybe, if proxy_server is not empty but doesn't have a scheme (e.g. proxy.example.com:3128, not http://proxy.example.com:3128, the module would consider http as a default scheme?