Unexpected error: delete bucket: incompatible value

[d2r2]

If at least one element added to the bucket with a value equal to null, then deleting this bucket will raise error: "delete bucket: incompatible value".

Code which reproduce the issue:

package main

import (
	"fmt"

	bolt "go.etcd.io/bbolt"
)

// Error description:
//      If at least one element added to the bucket with a value equal to null,
//      then deleting this bucket will raise error: "delete bucket: incompatible value".
func main() {
	db, _ := bolt.Open("/tmp/bolt.db", 0666, nil)
	defer db.Close()
	tx, _ := db.Begin(true)
	defer tx.Rollback()

	bucketName := []byte("oops")
	b, _ := tx.CreateBucket(bucketName)

	// putting element with empty value works fine
	b.Put([]byte("any_key"), nil)

	// trying to delete bucket with unexpected error
	fmt.Println(tx.DeleteBucket(bucketName))
}

// Error output:
//      delete bucket: incompatible value

[d2r2]

#209 has been merged, so the issue is resolved.