[mariodavid]

Problem

The MCP schema converter reads a single entry from OpenAPI 3.1's Schema#getTypes(). A request property declared as ["string", "null"] loses one of its allowed types in the generated MCP inputSchema.

Fix

Emit a JSON Schema type array when the OpenAPI schema has multiple types. The existing single-type and OpenAPI 3.0 nullable: true paths still apply.

Tests

• OpenApiSchemaConverterTest#testOpenApi31TypeArraysInRequestBody parses a request body and verifies both ["string", "null"] and ["integer", "string"]. It fails on the old converter.
• ./mvnw -pl springdoc-openapi-starter-common-mcp -am test passes, including all 35 MCP module tests.
• A local Notes API E2E scenario verifies the generated OpenAPI contract and the types advertised over MCP, sends explicit content: null, and reads the saved note back.

Fixes #3427.