I turned edge labels on, they're using two String fields from each edge, but the labels aren't displaying and I get this exception:

java.lang.NullPointerException
at sun.font.FontDesignMetrics.stringWidth(FontDesignMetrics.java:459)
at org.gephi.preview.plugin.renderers.EdgeLabelRenderer.renderProcessing(EdgeLabelRenderer.java:233)
at org.gephi.preview.plugin.renderers.EdgeLabelRenderer.render(EdgeLabelRenderer.java:217)
at org.gephi.preview.PreviewControllerImpl.render(PreviewControllerImpl.java:258)
at org.gephi.preview.PreviewControllerImpl.render(PreviewControllerImpl.java:222)
at org.gephi.preview.ProcessingApplet.draw(ProcessingApplet.java:134)
at processing.core.PApplet.handleDraw(Unknown Source)
at processing.core.PApplet.run(Unknown Source)
[catch] at java.lang.Thread.run(Thread.java:619)