Introduce TimeRange::EMPTY
Merge branch 'master' into null-object
Merge branch 'master' into null-object

Conflicts:
	spec/time_frame_spec.rb
Fix rubocop issues
Fix specs for #deviation_of
Merge branch 'master' into null-object
Merge branch 'master' into null-object
Fix remaining RSpec3-incompatible specs
Merge branch 'master' into null-object
Fixed spec syntax
deviation_of raises error when used with Empty instances
Increased version
Reverted changed behaviour of deviation_of
Set error type
Merge pull request #6 from injixo/null-object

Null object