Fixes #4518: don't fail with exception if the key in <CFKEY> is empty
Merge pull request #30 from fanf/bug_4518/do_not_add_empty_cfengine_key

Fixes #4518: don't fail with exception if the key in <CFKEY> is empty
Merge branch 'branches/rudder/2.6' into branches/rudder/2.8
Merge branch 'branches/rudder/2.8' into branches/rudder/2.9