What causes "Nil callback provided to CommitWith" in dgraph-io/badger?

Pass a real callback: txn.CommitWith(func(err error){ ... })

Nil callback provided to CommitWith

Error message

Nil callback provided to CommitWith

What it means

CommitWith requires a callback because the commit result is delivered asynchronously via a goroutine. If you pass nil, Badger panics immediately at the public API boundary so the problem is caught before any commit work starts. Use Commit instead if you don't need a callback.

Source

Thrown at txn.go:702

	case cb.user == nil:
		panic("Must have caught a nil callback for txn.CommitWith")
	case cb.err != nil:
		cb.user(cb.err)
	case cb.commit != nil:
		err := cb.commit()
		cb.user(err)
	default:
		cb.user(nil)
	}
}

// CommitWith acts like Commit, but takes a callback, which gets run via a
// goroutine to avoid blocking this function. The callback is guaranteed to run,
// so it is safe to increment sync.WaitGroup before calling CommitWith, and
// decrementing it in the callback; to block until all callbacks are run.
func (txn *Txn) CommitWith(cb func(error)) {
	if cb == nil {
		panic("Nil callback provided to CommitWith")
	}

	if len(txn.pendingWrites) == 0 {
		// Do not run these callbacks from here, because the CommitWith and the
		// callback might be acquiring the same locks. Instead run the callback
		// from another goroutine.
		go runTxnCallback(&txnCb{user: cb, err: nil})
		// Discard the transaction so that the read is marked done.
		txn.Discard()
		return
	}

	// Precheck before discarding txn.
	if err := txn.commitPrecheck(); err != nil {
		cb(err)
		return
	}

View on GitHub (pinned to 2a001d466f)

Solutions

Pass a real callback: txn.CommitWith(func(err error){ ... })
If no callback is needed, call txn.Commit() instead
Guard wrappers: if cb == nil { return txn.Commit() }; txn.CommitWith(cb)

Example fix

// before
txn.CommitWith(nil)
// after
txn.CommitWith(func(err error) {
    if err != nil { log.Printf("commit failed: %v", err) }
})

Defensive patterns

Strategy: validation

Validate before calling

if cb == nil { return errors.New("callback required; use txn.Commit() if none needed") }
txn.CommitWith(cb)

Try / catch

defer func(){ if r := recover(); r != nil { if s, ok := r.(string); ok && strings.Contains(s, "Nil callback") { log.Error(s) } } }()

Prevention

Default to txn.Commit() when no async handling is needed
Never forward nil callbacks through generic wrappers
Initialize callback variables with a no-op func rather than leaving them nil

When it happens

Trigger: Calling txn.CommitWith(nil), or passing a variable holding a nil func(error) (including a typed-nil function value).

Common situations: Conditional callback assignment where the variable ends up nil; refactoring from Commit to CommitWith and forgetting to supply the callback; generic wrapper code that forwards a nil cb.

Related errors

AI-assisted analysis of dgraph-io/badger@2a001d466f (2026-09-05). Data as JSON: /api/errors/b66ee48e324822f2. Report an issue: GitHub.