Prevent Duplicate Nicknames

[SuperYoshi10000]

Don't let multiple people have the same nicknames, because this has been used for impersonation

[sentry]

Bug: NullPointerException when getNickname().equals() is called on a null nickname in NickCommand's findData predicate.
_{Severity: CRITICAL | Confidence: 1.00}

🔍 Detailed Analysis

A NullPointerException occurs when NickCommand attempts to find an existing nickname using plugin.getDataManager().findData(). The predicate data -> data.getNickname().equals(newNickname) will invoke .equals() on a null object if any online player has not yet set their nickname (as nickname defaults to null). This unhandled exception crashes the server. A similar vulnerability exists in SlackBot.java line 319 where pData.getSlackId().equals(id) can also cause a NullPointerException if slackId is null.

💡 Suggested Fix

Before calling .equals() on data.getNickname(), ensure data.getNickname() is not null. A safe check would be newNickname.equals(data.getNickname()) or data.getNickname() != null && data.getNickname().equals(newNickname).

🤖 Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: src/main/java/com/hackclub/hccore/commands/NickCommand.java#L46

Potential issue: A NullPointerException occurs when `NickCommand` attempts to find an
existing nickname using `plugin.getDataManager().findData()`. The predicate `data ->
data.getNickname().equals(newNickname)` will invoke `.equals()` on a `null` object if
any online player has not yet set their nickname (as `nickname` defaults to `null`).
This unhandled exception crashes the server. A similar vulnerability exists in
`SlackBot.java` line 319 where `pData.getSlackId().equals(id)` can also cause a
NullPointerException if `slackId` is `null`.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

_{Reference_id: 2711684}

[aelithron]

oh, that's what that workflow does :heavysob:
looks good overall so i will approve it, won't merge yet but soon

[aelithron]

Please null-check as Sentry mentioned, I think this could lead to a problem where people can't set nicknames and a NullPointerException happens.