Error in display_constraints_with_extreme_jacobians when a constraint has no unfixed variables #1644
Description
An IDAES user encountered a math domain error in display_constraints_with_extreme_jacobians when trying to debug his model. This error was caused by an inequality constraint with zero unfixed variables. The Jacobian row corresponding to this constraint had zero norm and therefore caused a domain error when we take the log of the norm to sort rows. It's unclear whether this constraint ever got passed to IPOPT or whether Pyomo silently dropped it, but it was visible to Pynumero when computing the Jacobian. At any rate, we'll need to manually screen for rows with zero norm.