Error with rbt = sympybotics.RobotDynCode(rbtdef, verbose=True) #26

Hi,

I am trying to run the example code step by step in the Python Shell.
When I put rbt = sympybotics.RobotDynCode(rbtdef, verbose=True), I got the following errors.
Please give me any advice to fix this issue.

generating geometric model
generating kinematic model
generating inverse dynamics code
Traceback (most recent call last):
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\SymPyBotics\example\kuka_dynamics.py", line 16, in
rbt = sympybotics.RobotDynCode(rbtdef, verbose=True)
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\robotmodel.py", line 58, in init
self.dyn.gen_invdyn(invdyn_se.collect)
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\dynamics\dynamics.py", line 22, in gen_invdyn
self.invdyn = rne(self.rbtdef, self.geom, ifunc)
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\dynamics\rne.py", line 29, in rne
fw_results = rne_forward(rbtdef, geom, ifunc)
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\dynamics\rne.py", line 15, in rne_forward
return rne_forward(rbtdef, geom, ifunc)
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\dynamics\rne_park.py", line 50, in rne_park_forward
V[i] = ifunc(Adj(geom.Tdh_inv[i], V[i - 1])) +
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\symcode\subexprs.py", line 170, in collect
out_exprs = list(map(self._parse, prep_exprs))
File "C:\Users\ymcho\AppData\Local\Programs\Python\Python37\lib\site-packages\sympybotics\symcode\subexprs.py", line 142, in _parse
if sympy.iterables.iterable(expr):
AttributeError: module 'sympy' has no attribute 'iterables'