[BUG][Rust] NullPointerException naming a oneOf member that has no title or type

[HardMax71]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

RustClientCodegen.fromModel names an inline oneOf member from its title, falling back to its type. A member with neither, such as allOf with a single $ref plus required, gets toModelName(null), and generation stops with a NullPointerException. GitHub's current REST description hits this on actions-policy-repo-conditions, so the rust generator can't produce a client for it.

The frame is the same as #21192, but that issue's own repro (a 3.1 anyOf with type: "null") generates fine on 7.25.0. This is a different trigger reaching the same line.

openapi-generator version

7.25.0, and master at 10e6c21.

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: oneOf member without a type
  version: "1"
paths:
  /conditions:
    get:
      operationId: getConditions
      responses:
        "200":
          description: ok
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Conditions"
components:
  schemas:
    Conditions:
      type: object
      oneOf:
        - type: object
          maxProperties: 0
        - allOf:
            - $ref: "#/components/schemas/WorkflowPathCondition"
          required:
            - workflow_path
          maxProperties: 1
    WorkflowPathCondition:
      type: object
      properties:
        workflow_path:
          type: string

Generation Details

java -jar openapi-generator-cli-7.25.0.jar generate -g rust -i spec.yaml -o out

Steps to reproduce

Exception in thread "main" java.lang.RuntimeException: Could not process model 'Conditions'.Please make sure that your schema is correct!
Caused by: java.lang.NullPointerException: Cannot invoke "String.replaceAll(String, String)" because "name" is null
	at org.openapitools.codegen.languages.AbstractRustCodegen.sanitizeIdentifier(AbstractRustCodegen.java:189)
	at org.openapitools.codegen.languages.AbstractRustCodegen.toModelName(AbstractRustCodegen.java:355)
	at org.openapitools.codegen.languages.RustClientCodegen.fromModel(RustClientCodegen.java:324)

Expected: a variant named after the member's base type, WorkflowPathCondition(Box<models::WorkflowPathCondition>).

Related issues/PRs

#21192 (same NullPointerException site).