hi there,I’m writing a plugin for GH using c# in Visual Studio，but I’m stuck in “curve union failed” for a while,please help me 
Curves are all planar,same height and closed,several curves intersect with each other.When I use"Curve.CreateBooleanUnion" API,sometimes It suceed,but sometimes It failed.I couldn’t figure out the reason.
Success (below):green outline:
Failure(below):green outline:
