to_poly_solve can return erroneous error

[kcrisman]

var('beta,N_0,V')
V = 1/2
N = 50
solve(exp(-beta*N_0)*(1/beta*N_0) + 1 - 1/(beta*N_0) - V, beta, to_poly_solve='force')

returns the empty solution set, but

var('beta,N_0,V')
V = 1/2
N = 50
solve(exp(-beta*N_0)*(1/beta*N_0) + 1 - 1/(beta*N_0) - V, beta, to_poly_solve=True)

gives a traceback

----> 4 solve(exp(-beta*N_0)*(Integer(1)/beta*N_0) + Integer(1) - Integer(1)/(beta*N_0) - V, beta, to_poly_solve=True)

/home/sc_serv/sage/local/lib/python2.7/site-packages/sage/symbolic/relation.pyc in solve(f, *args, **kwds)
    812     from sage.symbolic.expression import is_Expression
    813     if is_Expression(f): # f is a single expression
--> 814         ans = f.solve(*args,**kwds)
    815         return ans
    816 

/home/sc_serv/sage/src/sage/symbolic/expression.pyx in sage.symbolic.expression.Expression.solve (/home/sc_serv/sage/src/build/cythonized/sage/symbolic/expression.cpp:59288)()
  10983                             X.append(eq) # we keep this implicit solution
  10984                     else:
> 10985                         raise
  10986 
  10987         # make sure all the assumptions are satisfied

/home/sc_serv/sage/src/sage/symbolic/expression.pyx in sage.symbolic.expression.Expression.solve (/home/sc_serv/sage/src/build/cythonized/sage/symbolic/expression.cpp:59055)()
  10973                     s = m.to_poly_solve(x, options='algexact:true')
  10974                     T = string_to_list_of_solutions(repr(s))
> 10975                     X.extend([t[0] for t in T])
  10976                 except TypeError as mess:
  10977                     if ignore_exceptions:

TypeError: 'sage.symbolic.expression.Expression' object does not support indexing

My guess is that somehow whatever list of solutions is gotten isn't subdivided in the way expected here. We should at the very least catch this, if not fix it completely.

[kcrisman]

I suspect this is the same as #20436. If you agree, please set to positive review.

[bruno]

I agree.

[embray]

Closing tickets in the sage-duplicate/invalid/wontfix module with positive_review (i.e. someone has confirmed they should be closed).