Bug: Plugin not being able to read CustomModel data.

### In which plugin has the error occurred?

FancyNpcs

### What happened?

When i start my servers the npcs arent there and this pops up in my console constantly.

### In which software has the error occurred?

Paper

### Plugin version

2.5.1

### Server version

1.21.3

### Relevant log output

```shell
[19:25:36 WARN]: [FancyNpcs] Task #217 for FancyNpcs v2.5.1 generated an exception
org.yaml.snakeyaml.error.YAMLException: Could not deserialize object
at org.bukkit.configuration.file.YamlConstructor$ConstructCustomObject.construct(YamlConstructor.java:60) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructObjectNoCheck(BaseConstructor.java:264) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructObject(BaseConstructor.java:247) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructMapping2ndStep(BaseConstructor.java:576) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.SafeConstructor.constructMapping2ndStep(SafeConstructor.java:210) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructMapping(BaseConstructor.java:552) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.SafeConstructor$ConstructYamlMap.construct(SafeConstructor.java:597) ~[snakeyaml-2.2.jar:?]
at org.bukkit.configuration.file.YamlConstructor$ConstructCustomObject.construct(YamlConstructor.java:49) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructObjectNoCheck(BaseConstructor.java:264) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructObject(BaseConstructor.java:247) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructMapping2ndStep(BaseConstructor.java:576) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.SafeConstructor.constructMapping2ndStep(SafeConstructor.java:210) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructMapping(BaseConstructor.java:552) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.SafeConstructor$ConstructYamlMap.construct(SafeConstructor.java:597) ~[snakeyaml-2.2.jar:?]
at org.bukkit.configuration.file.YamlConstructor$ConstructCustomObject.construct(YamlConstructor.java:49) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructObjectNoCheck(BaseConstructor.java:264) ~[snakeyaml-2.2.jar:?]
at org.yaml.snakeyaml.constructor.BaseConstructor.constructObject(BaseConstructor.java:247) ~[snakeyaml-2.2.jar:?]
at org.bukkit.configuration.file.YamlConstructor.construct(YamlConstructor.java:37) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConfiguration.fromNodeTree(YamlConfiguration.java:164) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConfiguration.fromNodeTree(YamlConfiguration.java:162) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConfiguration.fromNodeTree(YamlConfiguration.java:162) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConfiguration.fromNodeTree(YamlConfiguration.java:162) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConfiguration.loadFromString(YamlConfiguration.java:121) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.FileConfiguration.load(FileConfiguration.java:160) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.FileConfiguration.load(FileConfiguration.java:128) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConfiguration.loadConfiguration(YamlConfiguration.java:310) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at FancyNpcs-2.5.1.jar/de.oliver.fancynpcs.NpcManagerImpl.loadNpcs(NpcManagerImpl.java:227) ~[FancyNpcs-2.5.1.jar:?]
at FancyNpcs-2.5.1.jar/de.oliver.fancynpcs.FancyNpcs.lambda$onEnable$2(FancyNpcs.java:284) ~[FancyNpcs-2.5.1.jar:?]
at org.bukkit.craftbukkit.scheduler.CraftTask.run(CraftTask.java:78) ~[paper-1.21.3.jar:1.21.3-83-d6c81da]
at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:474) ~[paper-1.21.3.jar:1.21.3-83-d6c81da]
at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:1804) ~[paper-1.21.3.jar:1.21.3-83-d6c81da]
at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:1665) ~[paper-1.21.3.jar:1.21.3-83-d6c81da]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1330) ~[paper-1.21.3.jar:1.21.3-83-d6c81da]
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:340) ~[paper-1.21.3.jar:1.21.3-83-d6c81da]
at java.base/java.lang.Thread.run(Thread.java:1583) ~[?:?]
Caused by: java.lang.IllegalArgumentException: Specified class does not exist ('CustomModelData')
at org.bukkit.configuration.serialization.ConfigurationSerialization.deserializeObject(ConfigurationSerialization.java:199) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
at org.bukkit.configuration.file.YamlConstructor$ConstructCustomObject.construct(YamlConstructor.java:58) ~[paper-api-1.21.3-R0.1-SNAPSHOT.jar:?]
... 34 more
```