<!-- SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder SPDX-License-Identifier: CC0-1.0 --> <!-- This form is for bug reports ONLY! If you're looking for help check out the [readme](/README.md). --> **Bug report** **What happened / Problem description**: I tried to use the `MultiDomainNewtonConvergenceWriter` but encountered a segmentation fault due to a null ptr exception. **What you expected to happen**: I expected the compiled program to run without a segmentation fault. **How to reproduce it (as minimally and precisely as possible)**: Instantiate the `MultiDomainNewtonConvergenceWriter` for a multi-domain problem and attach the writer to the `NewtonSolver`, see #1365. Compile and run the program, calling the `solve` method of the NewtonSolver. **Anything else we need to know?**: The bug is caused by the following line: https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/-/blob/7e8c2744b2b69db3357390970748c8cd92dc6b21/dumux/multidomain/newtonconvergencewriter.hh#L68 It can be solved by - a quick fix: changing `gridGeometryTuple` to `gridGeometryTuple_` in L68 - a change of the member variable `GridGeometryTuple gridGeometryTuple_;` of `MultiDomainNewtonConvergenceWriter` to a const ref (or shared_ptr) just like in `NewtonConvergenceWriter`. This would mean also removing the `std::move(...)` in the initializer list to not destroy the original object. **Environment** - Dune version: 2.9 - DuMux version: 3.8 (master) - Others: