How to reproduce an error.

Create a project.

$ motion create static
$ cd static

Edit Gemfile. Just add a line gem 'motion-cocoapods'

source 'https://rubygems.org'

gem 'rake'
# Add your dependencies here:

gem 'motion-cocoapods'

Make static library.

$ bundle
$ rake pod:install
$ rake static

Got an error.

TypeError: no implicit conversion of nil into String
/Users/ISD/.rubymotion/rubymotion-templates/motion/project/template/ios.rb:345:in `+'
/Users/ISD/.rubymotion/rubymotion-templates/motion/project/template/ios.rb:345:in `block (2 levels) in <top (required)>'
/Users/ISD/.rubymotion/rubymotion-templates/motion/project/template/ios.rb:344:in `map'
/Users/ISD/.rubymotion/rubymotion-templates/motion/project/template/ios.rb:344:in `block in <top (required)>'
Tasks: TOP => static
(See full trace by running task with --trace)