Exception when trying to perform a pdf export: java.lang.NoClassDefFoundError: org/apache/fop/fonts/CustomFontCollection

Wrapped Exception:

java.lang.NoClassDefFoundError: org/apache/fop/fonts/CustomFontCollection
at org.apache.fop.render.PrintRendererConfigurator.setupFontInfo(PrintRendererConfigurator.java:129)
at org.apache.fop.render.intermediate.IFUtil.setupFonts(IFUtil.java:165)
at org.apache.fop.render.intermediate.IFRenderer.setupFontInfo(IFRenderer.java:180)
at org.apache.fop.area.RenderPagesModel.(RenderPagesModel.java:73)
at org.apache.fop.area.AreaTreeHandler.setupModel(AreaTreeHandler.java:130)
at org.apache.fop.area.AreaTreeHandler.(AreaTreeHandler.java:102)
at org.apache.fop.render.RendererFactory.createFOEventHandler(RendererFactory.java:359)
at org.apache.fop.fo.FOTreeBuilder.(FOTreeBuilder.java:105)
at org.apache.fop.apps.Fop.createDefaultHandler(Fop.java:100)
at org.apache.fop.apps.Fop.(Fop.java:78)
at org.apache.fop.apps.FopFactory.newFop(FopFactory.java:253)
at com.xpn.xwiki.pdf.impl.PdfExportImpl.exportXMLFO(PdfExportImpl.java:198)
at com.xpn.xwiki.pdf.impl.PdfExportImpl.exportXHtml(PdfExportImpl.java:185)
at com.xpn.xwiki.pdf.impl.PdfExportImpl.exportHtml(PdfExportImpl.java:235)
at com.xpn.xwiki.pdf.impl.PdfExportImpl.export(PdfExportImpl.java:266)