I’m the author of SymbolicWedderburn.jl 
and sorry for taking time of everybody here ;D, but the problem is very simple:
@Khashayar-Neshat You’re trying to run examples from master branch while using the released version of the package. This is bound to fail, given the number of changes in the current master.
as I’ve already stated, I only haphazardly update examples folder while developing the next release.
If you can’t make them work, it’d be better to open an issue in the repository directly.