bug when spawning mobs

[Trirly]

sometimes, when a structure is created, either by command or by world generation, the mobs placed on signs do not spawn, sometimes spawn 2/3 mobs, other times none, it is a very inconsistent bug

Steps to Reproduce
Create scheme with signs for vanilla mobs and mythicmobs with range of number of mobs to spawn

Expected behavior
spawn all mobs in range

Environment Information:

• Minecraft Version: 1.18.1
• Spigot Version: paper-1.18.1-216
• Custom Structures Version: 1.8.2
• World Edit Version: 7.2.10

I don't know if it has to do but
when I use the command /cstructure test {Structure Name}
(obviously with the name of the structure) in the console I get this error:

[WARN]: [CustomStructures] Task #21241 for CustomStructures v1.8.2 generated an exception
java.lang.NullPointerException: Cannot invoke "java.util.Map$Entry.getValue()" because the return value of "java.util.NavigableMap.higherEntry(Object)" is null
at com.ryandw11.structure.utils.RandomCollection.next(RandomCollection.java:86) ~[CustomStructures-1.8.2.jar:?]
at com.ryandw11.structure.SchematicHandler.replaceContainerContent(SchematicHandler.java:592) ~[CustomStructures-1.8.2.jar:?]
at com.ryandw11.structure.SchematicHandler.lambda$schemHandle$0(SchematicHandler.java:212) ~[CustomStructures-1.8.2.jar:?]
at org.bukkit.craftbukkit.v1_18_R1.scheduler.CraftTask.run(CraftTask.java:101) ~[paper-1.18.1.jar:git-Paper-216]
at org.bukkit.craftbukkit.v1_18_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:483) ~[paper-1.18.1.jar:git-Paper-216]
at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:1557) ~[paper-1.18.1.jar:git-Paper-216]
at net.minecraft.server.dedicated.DedicatedServer.tickChildren(DedicatedServer.java:480) ~[paper-1.18.1.jar:git-Paper-216]
at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:1480) ~[paper-1.18.1.jar:git-Paper-216]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1273) ~[paper-1.18.1.jar:git-Paper-216]
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:317) ~[paper-1.18.1.jar:git-Paper-216]
at java.lang.Thread.run(Thread.java:833) ~[?:?]