install_sources command bug: no implicit conversion of nil into String

Log:

$ pod_builder install_sources
Updating local specs repositories

CocoaPods 1.10.0.rc.1 is available.
To update use: `sudo gem install cocoapods --pre`
[!] This is a test version we'd love you to try.

For more information, see https://blog.cocoapods.org and the CHANGELOG for this version at https://github.com/CocoaPods/CocoaPods/releases/tag/1.10.0.rc.1

Analyzing dependencies
Checking out SnapKit
no implicit conversion of nil into String
/Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/lib/pod_builder/command/install_sources.rb:51:in `system'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/lib/pod_builder/command/install_sources.rb:51:in `update_repo'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/lib/pod_builder/command/install_sources.rb:22:in `block in call'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/lib/pod_builder/command/install_sources.rb:18:in `each'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/lib/pod_builder/command/install_sources.rb:18:in `call'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/exe/pod_builder:362:in `block in parse_commandline'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/exe/pod_builder:361:in `each'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/exe/pod_builder:361:in `parse_commandline'
    /Library/Ruby/Gems/2.6.0/gems/pod-builder-1.9.4/exe/pod_builder:379:in `<top (required)>'
    /usr/local/bin/pod_builder:23:in `load'
    /usr/local/bin/pod_builder:23:in `<main>'

Command failed!

Env:

$ ruby -v
ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin19]

$ pod_builder --version
1.9.4

Subito-it / PodBuilder

install_sources command bug: no implicit conversion of nil into String #15