I am facing same issue. I am using Fusionchart 3.3.
Error is on line # 266 in FusionCharts.HC.js.
Statement that is giving error is "c.paper.defs.appendChild(i)", where c.paper.defs object is null.
This is the call trace:
Uncaught TypeError: Cannot read property 'appendChild' of null
window.Raphael.svg.d._setFillAndStroke @ FusionCharts.HC.js:266
window.Raphael.svg.u.attr @ FusionCharts.HC.js:285
V.createSlice.b @ FusionCharts.HC.Charts.js:104
V.updateSliceConf @ FusionCharts.HC.Charts.js:90
V.createSlice.b @ FusionCharts.HC.Charts.js:104
kb @ FusionCharts.HC.js:239
Also when I load page first time, I get "c.paper.defs" object filled as "[object SVGDefsElement]" and graph renders right.
However when I try to rerender graph by calling "FusionCharts(chartId).render();" statement on button click, I receive "c.paper.defs" as null and hence the error.