bound_emission values equal to 0 disappear in output GDX

Hey, I am just doing some model runs where I limit emissions in a certain period to 0. The emission bound is considered in some way (however, the emissions are fully not reduced to 0) but also the bound parameter itself is not portrayed in the output gdx (I guess 0 are not passed through?). This is not a big issue, however it is somewhat inconsistent, if the solution is calculated considering the bound but the bound itself is not to be found in the output gdx.

Reproduce a model run with an emissions limit of 0 and inspect the resulting output GDX, comparing the bound parameter with the calculated emissions. Trace where zero-valued bounds are selected for output and confirm that the bound remains present while the model still respects it.

Written by the indexing model from the issue text.