Malformed Json in NBT tag of a spawn_egg used in a dispenser makes the server crash (JsonSyntaxException, MalformedJsonException)

A player on my server managed to make my server crash (1.15.2, Spigot) exploiting a bug that I managed to reproduce on vanilla Minecraft (see attached crash reports).

The bug

The player was in creative mode, he used a creeper_spawn_egg with some NBT (see screenshot), that he put in a dispenser and activated it with a redstone signal (lever, button, or whatever). This action crashes the server and generate a crash report that you can see attached.

This bug is also reproductible in single player, making Minecraft crash completely.

How to reproduce

• Give yourself this creeper egg :
  • /give @p minecraft:creeper_spawn_egg{EntityTag:{CustomName:"NotJson",CustomNameVisible:1}} 1
• Put the egg in a dispenser.
• Activate that dispenser with a lever.
• The server will crash and a crash report will be generated