If you have a pipeline with an empty branch name, it will fail to visualise. This could be a data problem or front end codes expectation. 

In any case to reproduce, create a pipeline with: 

node {

stage('first') {
sh 'echo hey'
}
stage('middle') {
parallel(
"top" : { sh 'echo there' },
"" : { echo 'empty one' }
)
}

}

And then look at the visualisation. You wil see it fails to render with an error message:

"Error rendering PipelineRunGraph: Error: convertJenkinsNodeDetails: malformed / missing Jenkins run node."