Relationships with no properties defined are no longer ignored

When using the following YAML configuration, the edges were not added to the graph. The PR fixes this issue: 

    connection:
      scheme: http
      host: localhost
      port: 7474
    
    nodes:
      users:
        label: User
        count: 5
        properties:
          email: email
        
      fileSpaces:
          label: FileSpace
          count: 5
    
    relationships:
      fileSpaceRels:
        start: User
        end: FileSpace
        type: FILESPACE
        mode: 1..1