The Mud Brick Double Slab has no name.

In all languages the block would have a name but it will never be displayed because of a spelling error.
'tile.mud_brick_double_slab.name' is misspelled as 'tile.mud_brick_double_slab'.
This effects all 29 languag files

In the atachment you can see the problem and how it is supposed to look when corrected with a Resource Pack.

Repro steps:
1. Place two Mud Brick Slabs in one block to create a Mud Brick Double Slab.
2. Stand on top of the double slab.
3. Use the '/testforblock ~ ~-1 ~ air' command.