Uninitialized constant OpenTelemetry::Context::Propagation::DefaultSetter

[sj26]

The datadog exporter cannot be used with current opentelemetry gems. It raises an error during load:

.../opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog/propagator.rb:17:in `<class:Propagator>':
uninitialized constant OpenTelemetry::Context::Propagation::DefaultSetter (NameError)

bundle show | egrep "opentelemetry|ddtrace"
  * ddtrace (0.49.0)
  * opentelemetry-api (0.17.0)
  * opentelemetry-common (0.17.0)
  * opentelemetry-exporters-datadog (0.1.0)
  * opentelemetry-sdk (0.17.0)

To Reproduce

Within a rails app, add the gems:

bundle add opentelemetry-sdk opentelemetry-exporters-datadog

Then boot the rails application.

bin/rails runner true

The exception is raised while loading:

/opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog/propagator.rb:17:in `<class:Propagator>': uninitialized constant OpenTelemetry::Context::Propagation::DefaultSetter (NameError)
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog/propagator.rb:16:in `<module:Datadog>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog/propagator.rb:14:in `<module:Exporters>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog/propagator.rb:13:in `<module:OpenTelemetry>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog/propagator.rb:12:in `<top (required)>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry/exporters/datadog.rb:16:in `<top (required)>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/opentelemetry-exporters-datadog-0.1.0/lib/opentelemetry-exporters-datadog.rb:8:in `<top (required)>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler/runtime.rb:66:in `require'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler/runtime.rb:66:in `block (2 levels) in require'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler/runtime.rb:61:in `each'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler/runtime.rb:61:in `block in require'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler/runtime.rb:50:in `each'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler/runtime.rb:50:in `require'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.20/lib/bundler.rb:174:in `require'
	from /Users/sj26/Developer/Buildkite/buildkite/config/application.rb:16:in `<top (required)>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application.rb:92:in `require'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application.rb:92:in `preload'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application.rb:157:in `serve'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application.rb:145:in `block in run'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application.rb:139:in `loop'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application.rb:139:in `run'
	from /opt/rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/spring-2.1.0/lib/spring/application/boot.rb:19:in `<top (required)>'
	from /opt/rbenv/versions/2.7.2/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:72:in `require'
	from /opt/rbenv/versions/2.7.2/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:72:in `require'
	from -e:1:in `<main>'

Expected behavior
The rails app should boot.