public Schema getSchema(String pointer) {
        return schemas.getDefinition(pointer)
                .orElseThrow(() -> new OpenApiException("Expected JSON schema definition not found: " + pointer));
    }
Gets a converted schema from the context object by JSON pointer
and throws if the schema does not exist.

@param pointer Schema to retrieve by JSON pointer (e.g., "#/components/schemas/foo").
@return Returns the found schema.
@throws OpenApiException if the schema cannot be found.
smithy-openapi/src/main/java/software/amazon/smithy/openapi/fromsmithy/Context.java