Steps to Reproduce

run the attached example
click button "(1) ..."

Current Result

initial chart rendering -> almost immediate
rendering after model was initally NULL (Button sequence: 1) -> slower
subsequent rendering after first time (Button sequence: 1 (slow) 1 1 1) -> fast
rendering after setting the model to NULL (Button sequence: 2 1 2 1 ...) -> slow (also causes NPEs)
rendering after setting an empty model (Button sequence: 3 1 3 1 ...) -> fast

Expected Result

the chart rendering should be equally fast when rendering the same data

Debug Info

check chrome profile for timing details

Root Cause

Workaround

avoid rendering a chart with a NULL model
-> at least set an empty model (e.g. new DefaultCategoryModel(); )