v1.2.0: introduce nullable

What's Changed

• add performance by @huykingsofm in #38
• introduce nullable by @huykingsofm in #39
• enhance README by @huykingsofm in #40
• fix typo by @huykingsofm in #41
• Merge dev by @huykingsofm in #42

Full Changelog: v1.1.1...v1.2.0