Pass `com.github.tomakehurst.wiremock.matching.StringValuePattern` to `com.github.tomakehurst.wiremock.client.MappingBuilder#withHeader(java.lang.String, com.github.tomakehurst.wiremock.matching.StringValuePattern)` from Spock's `where` clause to test header value set and absent

WireMockSpec.groovy

    def "fetch file info"() {

        given:
        UUID fileId = UUID.randomUUID()
        FileMetadata response = new FileMetadata(fileId, "/somePath", "someFileName.xls", 100)

        wireMockServer.stubFor(
            get(urlPathTemplate(uri))
                .withPathParam("fileId", equalTo(fileId.toString()))
                .withHeader(AUTHORIZATION_HEADER, expectedAuthorization)
                .withHeader(USER_ID_HEADER, expectedPassedUserId)
                .willReturn(okJson(json(response)))
        )

        when:
        Optional<FileMetadata> result = metadataFetcher.fetchFileInfo(portalType, fileId, authorization, passedUserId)

        then:
        result
        !wireMockServer.findUnmatchedRequests().requests

        where:
        authorization  | expectedAuthorization  | passedUserId | expectedPassedUserId
        null           | absent()               | null         | absent()
        null           | absent()               | "user"       | equalTo(passedUserId)
        "Bearer token" | equalTo(authorization) | null         | absent()
        "Bearer token" | equalTo(authorization) | "user"       | equalTo(passedUserId)
    }