In older worlds where people managed to make custom maps and placed them on large walls, in 1.14 they were still there, but in 1.15 and 1.15.1 the custom made maps are similar to a item frame only larger. When breaking it, it falls in your hand as an empty map!
Added picture shows a 4by3 custom made map and on the bottomline I show from left to right an itemframe, a custom made sign in 1.15.1 and two old ones, copied from older games and imported(thoses that were places in this (1.15) world are also blank!)