What causes "found invalid nulltime" in dgraph-io/dgraph?

Replace NULLs in the query with COALESCE(col, '1970-01-01 00:00:01') or filter out NULL rows.

found invalid nulltime

Error message

found invalid nulltime

What it means

For datetimeType columns the go-sql-driver returns mysql.NullTime; when Valid is false the cell is a NULL timestamp. getValue returns "found invalid nulltime" rather than emitting an empty/invalid datetime predicate.

Source

Thrown at dgraph/cmd/migrate/table_guide.go:167

}

func getValue(dataType dataType, value interface{}) (string, error) {
	if value == nil {
		return "", errors.Errorf("nil value found")
	}

	switch dataType {
	case stringType:
		return fmt.Sprintf("%s", value), nil
	case intType:
		if !value.(sql.NullInt64).Valid {
			return "", errors.Errorf("found invalid nullint")
		}
		intVal, _ := value.(sql.NullInt64).Value()
		return fmt.Sprintf("%v", intVal), nil
	case datetimeType:
		if !value.(mysql.NullTime).Valid {
			return "", errors.Errorf("found invalid nulltime")
		}
		dateVal, _ := value.(mysql.NullTime).Value()
		return fmt.Sprintf("%v", dateVal), nil
	case floatType:
		if !value.(sql.NullFloat64).Valid {
			return "", errors.Errorf("found invalid nullfloat")
		}
		floatVal, _ := value.(sql.NullFloat64).Value()
		return fmt.Sprintf("%v", floatVal), nil
	default:
		return fmt.Sprintf("%v", value), nil
	}
}

type ref struct {
	allColumns       map[string]*columnInfo
	refColumnIndices []*columnIdx
	tableName        string

View on GitHub (pinned to 759e242be6)

Solutions

Replace NULLs in the query with COALESCE(col, '1970-01-01 00:00:01') or filter out NULL rows.
Set a NOT NULL DEFAULT on the datetime column before migrating.
Patch getValue to skip invalid NullTime values if absent timestamps are acceptable in Dgraph.
Locate the offending column from the wrapped table name in the error chain.

Example fix

// before
SELECT id, completed_at FROM tasks; -- completed_at NULL
// after
SELECT id, COALESCE(completed_at, '1970-01-01 00:00:01') AS completed_at FROM tasks;

Defensive patterns

Strategy: validation

Validate before calling

-- find NULL datetimes in datetime-typed columns
SELECT id FROM tasks WHERE completed_at IS NULL;

Type guard

func validTime(v interface{}) bool {
	nt, ok := v.(mysql.NullTime)
	return ok && nt.Valid
}

Try / catch

if err := migrate.Run(); err != nil {
	if strings.Contains(err.Error(), "found invalid nulltime") {
		log.Printf("NULL datetime column detected: %+v", err)
	}
}

Prevention

COALESCE NULL timestamps to an epoch default in the query
Set NOT NULL DEFAULT on datetime columns
Check mysql.NullTime.Valid before using the time value

When it happens

Trigger: A column mapped to datetimeType in the table guide contains SQL NULL (mysql.NullTime{Valid:false}) and is read during dumpTable via outputPlainCell, generate, or createLabel.

Common situations: Nullable TIMESTAMP/DATETIME columns (e.g. optional deleted_at, completed_at) with NULL rows; legacy rows predating a column addition; imports that left timestamps unset.

Related errors

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/000686a55d5e394b. Report an issue: GitHub.