code: function formatTriplePattern (triple) {
    let subject = null
    let predicate = null
    let object = null
    if (!triple.subject.startsWith('?')) {
      subject = triple.subject
    }
    if (!triple.predicate.startsWith('?')) {
      predicate = triple.predicate
    }
    if (!triple.object.startsWith('?')) {
      object = triple.object
    }
    return { subject, predicate, object }
  }
docs: Format a triple pattern according to N3 API: SPARQL variables must be replaced by `null` values