fancysets: added support for Symbols
fancysets: added support for Symbols

Return `None` in case of symbols.
This allows to return the expression instead of a truth value.

yashsharan/sympy,kaushik94/sympy,yashsharan/sympy,kaushik94/sympy,chaffra/sympy,madan96/sympy,chaffra/sympy,chaffra/sympy,jaimahajan1997/sympy,skidzo/sympy,madan96/sympy,skidzo/sympy,jaimahajan1997/sympy,skidzo/sympy,madan96/sympy,jaimahajan1997/sympy,kaushik94/sympy,yashsharan/sympy