Gotta weigh in on this one. Pre-made blueberry pie filling is rather runny. Also, if you bake the pie without a crust, or topping of any kind, the surface layer of the filling may become somewhat rubbery as the moisture evaporates. Add just a little bit of a slurry of made from water and flour to the pie filling before you put it into the pie shell. And yes, the bottom pie crust should be pricked with a for, to prevent bubbling, and brushed with egg wash to seal it against the wet filling to insure a flaky bottom crust. Then put the filling in, cover with topping or top pie crust, poke vent holes in the top to let steam escape (if using a top crust), and bake at 375 for about 45 minutes.
For the slurry, use about t tbs flour combined with an equal amount of water. Make sure there are no lumps in it. Mix it into the pie filling completely.
Enjoy.
Seeeeeya; Goodweed of the North