NonlinearSolveBase: accept verbose=nothing as default NonlinearVerbosity()

[ChrisRackauckas-Claude]

Summary

Three solve entry points in lib/NonlinearSolveBase/src/solve.jl (top-level solve at lines 50, 194, 495) already normalize Bool and AbstractVerbosityPreset values of the verbose kwarg into a NonlinearVerbosity. Extend the branch set to also accept nothing, normalizing it to NonlinearVerbosity() (the default).

Why

Wrapping solves that forward a caller's verbose kwarg through to NonlinearSolve without owning the default may pass nothing to mean "inherit the default". Concrete call sites:

• DiffEqBase ↔ NonlinearSolve bridges used by stiff-ODE implicit solvers.
• SteadyStateDiffEq.SSRootfind.__solve forwards its kwargs directly to NonlinearSolve.solve (see Widen DiffEqBase compat to v7 (and tidy SciMLBase bound) SteadyStateDiffEq.jl#122 for the companion fix in the DynamicSS branch, where the inner kwargs go to an ODE solve instead).

Prior to this, a caller-forwarded verbose = nothing would skip both normalizing branches (Bool, AbstractVerbosityPreset), land in downstream verbose.display_level / verbose.convergence_failure field accesses, and fail with:

MethodError: no method matching getfield(::Nothing, …)

Fix

One new elseif verbose === nothing branch per solve entry point, converting to NonlinearVerbosity().

Version

Bumps NonlinearSolveBase to 2.25.1 (patch — additive, non-breaking).

[ChrisRackauckas-Claude]

Closing — making NonlinearSolveBase tolerant of verbose = nothing just hides the upstream bug (a caller forwarding an unset verbose as nothing when it should be passing an actual NonlinearVerbosity / DEVerbosity / Bool). Fix goes at the caller layer instead.