Zero value of a map is nil. It's length is 0.

https://codeeval.dev/gist/bdc98ebc675e6a251539afa1542d3235

Reading from a nil map behaves like reading from an empty map. Writing to a nil map crashes.

https://codeeval.dev/gist/3de2700bc20b6d3106a7a19e011c35a3