It wouldn't be a black hole, it'd be like pushing concrete into a slab of concrete. It just would take an insane amount of force to compress, and you'd have no leverage
Conversely, what's the range for taking things in and out?
What if you brought in extremely pressurized liquid air? Could you just take 1cc and release it next to someone's head? If you took open cones of tungsten in, you could probably abuse it to shoot them like a bullet
What about thermal properties? If the space wraps in on itself, there's nowhere for the heat to dissipate. You could fill it with extremely high temperature plasma, then take out a little at a time to melt/explode almost anything.
That all depends on the distance - you could fill it with thermite and burning magnesium for a trigger to fill it with extremely hot pressurized gas, but if you have to touch to take it out you'd destroy the body part that took it out... You could sacrifice a finger to blow up someone's head, but ultimately your power would stop at being a suicide bomber
Personally I wouldn't do any of that. It'd ruin the outlet