Forgetting mesh but still compute

Hello COMSOL

When i use AC/DC to compute the magnetic field, i forgot meshing one part of the permanent magnet, but the study can be computed without errors.

By checking the results, i found the part which was not meshed did not participate in computation.

Question: The part without meshing does not participate in computation? How can we avoid forgetting meshing when compute a common-used model?

Best

zhangxiang