Fix NPE when retrieving an entity with a null UUID

While the null UUID is almost certainly an error, the old
implementation did not NPE as it used a plain HashMap for lookup
by UUID, whereas we use a ConcurrentHashMap which will NPE on
null keys.

patches/server/0991-Chunk-System-Starlight-from-Moonrise.patch

@@ -5900,7 +5900,7 @@ index 0000000000000000000000000000000000000000..997b05167c19472acb98edac32d4548c
 +}
 diff --git a/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/EntityLookup.java b/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/EntityLookup.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..3a8c192d1aed186ff506d69e3960e3b2792ddbd1
+index 0000000000000000000000000000000000000000..f6a3eb3d1bb070bcc74133818682571d520d9894
 --- /dev/null
 +++ b/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/EntityLookup.java
 @@ -0,0 +1,1044 @@
@@ -5994,15 +5994,15 @@ index 0000000000000000000000000000000000000000..3a8c192d1aed186ff506d69e3960e3b2
 +
 +    @Override
 +    public Entity get(final UUID id) {
-+        return maskNonAccessible(this.entityByUUID.get(id));
++        return maskNonAccessible(id == null ? null : this.entityByUUID.get(id));
 +    }
 +
 +    public boolean hasEntity(final UUID uuid) {
 +        return this.get(uuid) != null;
 +    }
 +
 +    public String getDebugInfo() {
-+        return "count_id:" + this.entityById.size() + ",count_uuid:" + this.entityByUUID.size() + ",region_count:" + this.regions.size();
++        return "count_id:" + this.entityById.size() + ",count_uuid:" + this.entityByUUID.size() + ",count_accessible:" + this.getEntityCount() + ",region_count:" + this.regions.size();
 +    }
 +
 +    protected static final class ArrayIterable<T> implements Iterable<T> {