Parse error - Syntax Error GraphQL (12569:27) Unexpected Name "null"

I faced this error during the benchmark of GraphQL parsers in the wild.

Schema: https://github.com/StarpTech/graphql-parser-bench/blob/main/schema.graphql
Code: https://github.com/StarpTech/graphql-parser-bench/tree/main/go-graphql

```
❯ go run main.go
2021/08/14 19:58:09 Syntax Error GraphQL (12569:27) Unexpected Name "null"

12568: """
12569: packageName: String = null
^
12570: """
exit status 1
```