Fix another bug where usernames can be saved as null for FlatFileDB

src/main/java/com/gmail/nossr50/database/UserQueryUUIDImpl.java

@@ -0,0 +1,23 @@
+package com.gmail.nossr50.database;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+
+public class UserQueryUUIDImpl implements UserQueryUUID {
+    private final @NotNull UUID uuid;
+
+    public UserQueryUUIDImpl(@NotNull UUID uuid) {
+        this.uuid = uuid;
+    }
+
+    @Override
+    public @NotNull UserQueryType getType() {
+        return UserQueryType.UUID;
+    }
+
+    @Override
+    public @NotNull UUID getUUID() {
+        return uuid;
+    }
+}