Insert `Map` as `Json`

I have the schema

model Foo {
  id      Int   @id @default(autoincrement())
  fields  Json
}

model Foo {
  id      Int   @id @default(autoincrement())
  fields  Json
}

and I'd like to insert records with type

{ fields: Map<String, String> }[]

{ fields: Map<String, String> }[]

. However I'm getting an error

Type 'Map<string, string>' is not assignable to type 'JsonNull | InputJsonValue'

Type 'Map<string, string>' is not assignable to type 'JsonNull | InputJsonValue'

. How can I get around this?