Unexpected token at ''

[MarcBiosca]

Hi,
I'm trying to use slather to convert Xcode coverage output to Cobertura XML format.
The project contains both objective-c and swift files.

The output from Xcode seems OK, there is the profdata file which is not empty, also the .gcdo, .dia etc files...

But slather ends up with the below error:

Slathering...

Processing coverage file: /Users/marcbiosca/Library/Developer/Xcode/DerivedData/MobileSDK-cdwqzqnpwqkarzdkewkdznfastpf/Build/ProfileData/21968B43-AFA4-4330-B505-45D1D0DB1F57/Coverage.profdata
Against binary files:
	/Users/marcbiosca/Library/Developer/Xcode/DerivedData/MobileSDK-cdwqzqnpwqkarzdkewkdznfastpf/Build/Products/PlotDebug-iphonesimulator/libSelligentMobile.a

error: /Users/marcbiosca/Library/Developer/Xcode/DerivedData/MobileSDK-cdwqzqnpwqkarzdkewkdznfastpf/Build/Products/PlotDebug-iphonesimulator/libSelligentMobile.a: Failed to load coverage: No coverage data found
error: Could not load coverage information

/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/json/common.rb:156:in 'parse': 767: unexpected token at '' (JSON::ParserError)
	from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/json/common.rb:156:in 'parse'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/project.rb:135:in 'pathnames_per_binary'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/project.rb:124:in 'block in profdata_coverage_files'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/project.rb:123:in 'each'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/project.rb:123:in 'profdata_coverage_files'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/project.rb:98:in 'coverage_files'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/coverage_service/simple_output.rb:17:in 'post'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/command/coverage_command.rb:101:in 'post'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/lib/slather/command/coverage_command.rb:61:in 'execute'
	from /Library/Ruby/Gems/2.6.0/gems/clamp-1.3.2/lib/clamp/command.rb:66:in 'run'
	from /Library/Ruby/Gems/2.6.0/gems/clamp-1.3.2/lib/clamp/subcommand/execution.rb:18:in 'execute'
	from /Library/Ruby/Gems/2.6.0/gems/clamp-1.3.2/lib/clamp/command.rb:66:in 'run'
	from /Library/Ruby/Gems/2.6.0/gems/clamp-1.3.2/lib/clamp/command.rb:140:in 'run'
	from /Library/Ruby/Gems/2.6.0/gems/slather-2.7.2/bin/slather:17:in '<top (required)>'
	from /usr/local/bin/slather:23:in 'load'
	from /usr/local/bin/slather:23:in '<main>'

Any idea what could go wrong here?