Chromatic polynomial of a graph with loops

[Lluis Vena]

The output in sage of the function:

Graph([[1,1]],multiedges=True,loops=True).chromatic_polynomial()

(the chromatic polynomial of a vertex with a loop)

is:

x

but it seems to me that, if graphs with loops are allowed, then it should be

0

as there is no proper coloring

[slelievre]

Tracked at

- Sage Trac ticket 27966

  set chromatic number of looped graph to zero

  https://trac.sagemath.org/ticket/27966

This should be an easy ticket.