In the Flink docs, all formats document the "format" property as required. However, this is actually a property of the connector, not the format.
Prior to 1.12 this was only an issue for custom connectors as all of Flink's connectors by convention had a "format" property. With 1.12+, the Kafka connector made the "format" property non-required as users can instead use "value.format". Although being synonyms, this now logically breaks the documentation of the Formats stating that "format" is a required property.