Yard graph places class outside of it's module

Question

I have a ruby project with a module and a class defined in the module:

• a.rb
• a/b.rb

File a.rb contains:

require 'a/b'
module A
end

File a/b.rb contains:

module A
  class B
  end
end

When I run yardoc ** and then yard graph --full --dependencies | dot -T pdf -o doc/diagram.pdf, the resulting pdf contains class B, which is outside of module A.

However, in HTML files generated by yardoc the class B is correctly placed inside the module A.

How can I configure Yard such that the class B will be placed inside the module A?