title: Flutter Pod install failed - 'Invalid `Podfile` file no implicit conversion of nil into String
body: <p>I cloned the project for wearable
  <a href="https://github.com/sbis04/flutter_os_wear" rel="nofollow noreferrer">https://github.com/sbis04/flutter_os_wear</a></p>
  <p>Running pod install...
  CocoaPods' output:
  ↳</p>
  <pre><code>[!] Invalid `Podfile` file: no implicit conversion of nil into String.
  
   #  from /Volumes/Storage/Bottle/Wearables/flutter_os_wear/ios/Podfile:57
   #  -------------------------------------------
   #      unless File.exist?(copied_framework_path)
   &gt;        FileUtils.cp_r(File.join(cached_framework_dir, 'Flutter.framework'), copied_flutter_dir)
   #      end
   #  -------------------------------------------
  
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:301:in `rescue in block in from_ruby'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:295:in `block in from_ruby'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:50:in `instance_eval'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:50:in `initialize'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:293:in `new'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:293:in `from_ruby'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-core-1.9.3/lib/cocoapods-core/podfile.rb:259:in `from_file'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.9.3/lib/cocoapods/config.rb:200:in `podfile'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.9.3/lib/cocoapods/command.rb:150:in `verify_podfile_exists!'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.9.3/lib/cocoapods/command/install.rb:46:in `run'
  /Library/Ruby/Gems/2.6.0/gems/claide-1.0.3/lib/claide/command.rb:334:in `run'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.9.3/lib/cocoapods/command.rb:52:in `run'
  /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.9.3/bin/pod:55:in `&lt;top (required)&gt;'
  /usr/local/bin/pod:23:in `load'
  /usr/local/bin/pod:23:in `&lt;main&gt;'
  </code></pre>
  <p>Error output from CocoaPods:
  ↳
  Ignoring ffi-1.12.2 because its extensions are not built. Try: gem pristine ffi --version 1.12.2</p>