Error when data target is null

[kwokster10]

Tried generating and one of these for an app that contains models from Rails Engines. The html file was generated successfully after adding this patch: voormedia/rails-erd#70 (comment). However, there were json objects in data on L43 that has a target value of null, ex. {"source":400,"target":null,"color":1}.

Error in console:

erd.html:87 Uncaught TypeError: Cannot read property 'label' of undefined
    at SVGLineElement.<anonymous> (erd.html:87)
    at SVGLineElement.<anonymous> (d3.min.js:3)
    at zi.ey [as each] (d3.min.js:6)
    at zi.ry [as attr] (d3.min.js:6)
    at erd.html:87