GraphvizGrapher renderEdge throws NPE

I wanted to create a visualization of dependency for my guice bindings. I use the **GraphvizGrapher** to do that. I followed the another [SO question](https://stackoverflow.com/questions/9301007/is-there-any-way-to-get-guice-grapher-to-work) asked on this. But when I run that, I get `NPE` in **GraphvizGrapher**.

I am using guice 4.0. Below is the trace. I don't see much questions or information on Grapher and it never worked for me. Wondering if anyone uses it.

Exception in thread "main" java.lang.NullPointerException
at com.google.inject.grapher.graphviz.GraphvizGrapher.renderEdge(GraphvizGrapher.java:172)
at com.google.inject.grapher.graphviz.GraphvizGrapher.postProcess(GraphvizGrapher.java:85)
at com.google.inject.grapher.AbstractInjectorGrapher.graph(AbstractInjectorGrapher.java:112)
at com.google.inject.grapher.AbstractInjectorGrapher.graph(AbstractInjectorGrapher.java:102)
at com.amazon.imsreconciliation.modules.ModuleGraph.graph(ModuleGraph.java:24)
at com.amazon.imsreconciliation.modules.ModuleGraph.main(ModuleGraph.java:44)