OpenAPI: Mark StructField doc as nullable in REST catalog spec

[Amneet13]

Problem

The doc field in the StructField schema in rest-catalog-open-api.yaml was missing nullable: true. However, the Java implementation in Types.NestedField has always allowed doc to be null — it defaults to null (see Types.java line 761) and the doc() getter can return null.

This mismatch means clients that auto-generate code from the OpenAPI spec would incorrectly treat doc as a required non-null string, potentially causing deserialization failures when the server returns a StructField with no doc value.

Change

Added nullable: true to the doc field in the StructField schema to align the spec with the actual Java behavior.

References

• api/src/main/java/org/apache/iceberg/types/Types.java#L761
• open-api/rest-catalog-open-api.yaml#L2294

[singhpk234]

isn't this optional ?

iceberg/core/src/main/java/org/apache/iceberg/SchemaParser.java

Lines 92 to 94 in 1f0579f

	if (field.doc() != null) {
	generator.writeStringField(DOC, field.doc());
	}

while sending to server this is omitted ? i know while reading i.e fromJson we are null tolerant but i think its fine

[Amneet13]

@singhpk234 Thanks for the review! You're right that the Iceberg serializer omits doc when it's null. However, we ran into a real-world case where an Iceberg table is created on top of a Paimon table — in that scenario doc is explicitly sent as null (not omitted) in the response. This causes deserialization failures in clients auto-generated from the OpenAPI spec since the spec didn't allow null. Adding nullable: true makes the spec tolerant of both cases — absent and explicitly null — which is the safer contract for external clients.