api-guidelines/evolution/json.md

JSON Format Conventions

Any JSON-based message MUST conform to the following rules:

1. All JSON field names MUST follow the Naming Conventions (camelCase, American English etc.)
2. Field names MUST be ASCII alpha num characters, underscore (_) or dollar sign ($)
3. Boolean fields MUST NOT be of null value
4. Fields with null value SHOULD be omitted
5. Empty arrays and objects **SHOULD NOT ** be null (use [] or {} instead)
6. Array field names SHOULD be plural (e.g. "orders": [])