If you add a parallel branch of execution in the editor, add some steps, and save - it will save correctly, however it isn't a very good Jenkinsfile. 

Loading it up once it has completed a run will result in an error to visualise. The Jenkinsfile will end up looking like: 

Note that the branch name is empty string - this seems to upset declarative. I am not sure it executes that branch. 

stage('Static Analysis') {
steps {
parallel(
"Static Analysis": {
sh 'mvn findbugs:findbugs'
},
"": {
echo 'rewrewqrewq'
}
)
}
}
}

In any case, a branch should be required to be named, so I think this should be a validation error right? OR the editor should name that branch it creates. 

To reproduce: take an existing stage with at least one step, add a parallel branch, add steps to it (but do not name it)