Bug: Skins throwing errors

### In which plugin has the error occurred?

FancyNpcs

### What happened?

I've had two NPCs for a while and when I am trying to use '/npc skin npc8 LenaTheEevee' I get the following error:
```
[Thu 20:01:30 INFO ] [FancyNpcs] (FancyNpcs-Skins-0) WARN: Failed to fetch skin from Mojang API for ba728a0b-0c73-38e9-8964-9a5f947eb4ad
[Thu 20:01:30 INFO ] [FancyNpcs] (FancyNpcs-Skins-0) WARN: Cannot invoke "de.oliver.fancynpcs.skins.mojang.MojangAPI$RequestResponse.getProperty(String)" because "response" is null
[Thu 20:01:30 INFO ] java.lang.NullPointerException: Cannot invoke "de.oliver.fancynpcs.skins.mojang.MojangAPI$RequestResponse.getProperty(String)" because "response" is null
[Thu 20:01:30 INFO ] [FancyNpcs] (FancyNpcs-Skins-0) ERROR: Generated skin has no texture!
```
The funny part is that most other skins work except for 2.
What also confuses me is that the ID "ba728a0b-0c73-38e9-8964-9a5f947eb4ad" is not at all related to LenaTheEevee's UUID but I am not sure if it's supposed to be the UUID either.

The server is running in offline mode behind an online mode velocity proxy.

### In which software has the error occurred?

Paper

### Plugin version

2.7.0.287

### Server version

1.21.8

### Relevant log output

```shell
[Thu 20:01:30 INFO ] [FancyNpcs] (FancyNpcs-Skins-0) WARN: Failed to fetch skin from Mojang API for ba728a0b-0c73-38e9-8964-9a5f947eb4ad
[Thu 20:01:30 INFO ] [FancyNpcs] (FancyNpcs-Skins-0) WARN: Cannot invoke "de.oliver.fancynpcs.skins.mojang.MojangAPI$RequestResponse.getProperty(String)" because "response" is null
[Thu 20:01:30 INFO ] java.lang.NullPointerException: Cannot invoke "de.oliver.fancynpcs.skins.mojang.MojangAPI$RequestResponse.getProperty(String)" because "response" is null
[Thu 20:01:30 INFO ] [FancyNpcs] (FancyNpcs-Skins-0) ERROR: Generated skin has no texture!
```