Whenever a sign of any material of the mod is placed it crash the game, in singleplayer and in multiplayer.

Crash Logs
java.lang.NullPointerException: Cannot invoke "net.minecraft.class_4730.method_24145(net.minecraft.class_4597, java.util.function.Function)" because "$$7" is null
at net.minecraft.class_837.method_45800(class_837.java:101)
at net.minecraft.class_837.method_49920(class_837.java:81)
at net.minecraft.class_837.method_23083(class_837.java:66)
at net.minecraft.class_837.method_3569(class_837.java:41)
at net.minecraft.class_824.method_23079(class_824.java:90)
at net.minecraft.class_824.method_23081(class_824.java:79)
at net.minecraft.class_824.method_3554(class_824.java:104)
at net.minecraft.class_824.method_3555(class_824.java:79)
at net.minecraft.class_761.method_22710(class_761.java:1114)
at net.minecraft.class_757.method_3188(class_757.java:1087)
at net.minecraft.class_757.method_3192(class_757.java:850)
at net.minecraft.class_310.method_1523(class_310.java:1285)
at net.minecraft.class_310.method_1514(class_310.java:882)
at net.minecraft.client.main.Main.main(Main.java:256)
at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:480)
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74)
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)

-- Block Entity Details --
Details:
Name: regions_unexplored:sign_block_entity // net.regions_unexplored.block.entity.custom.RuSignBlockEntity
Block: Block{regions_unexplored:maple_wall_sign}[facing=west,waterlogged=false]
Block location: World: (10606,154,10614), Section: (at 14,10,6 in 662,9,663; chunk contains blocks 10592,-64,10608 to 10607,319,10623), Region: (20,20; contains chunks 640,640 to 671,671, blocks 10240,-64,10240 to 10751,319,10751)
Block: Block{regions_unexplored:maple_wall_sign}[facing=west,waterlogged=false]
Block location: World: (10606,154,10614), Section: (at 14,10,6 in 662,9,663; chunk contains blocks 10592,-64,10608 to 10607,319,10623), Region: (20,20; contains chunks 640,640 to 671,671, blocks 10240,-64,10240 to 10751,319,10751)
Stacktrace:
at net.minecraft.class_824.method_3554(class_824.java:104)
at net.minecraft.class_824.method_3555(class_824.java:79)
at net.minecraft.class_761.method_22710(class_761.java:1114)
at net.minecraft.class_757.method_3188(class_757.java:1087)
at net.minecraft.class_757.method_3192(class_757.java:850)
at net.minecraft.class_310.method_1523(class_310.java:1285)
at net.minecraft.class_310.method_1514(class_310.java:882)
at net.minecraft.client.main.Main.main(Main.java:256)
at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:480)
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74)
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)

How To Reproduce
Just place a sign

Version
Minecraft Version: 1.21

Mod Version: 0.5.6.1+1.21