generator = new TestThumbnailGenerator();

        // Setup mock FessConfig
        FessConfig mockConfig = new FessConfig.SimpleImpl() {
            @Override
            public String getIndexFieldThumbnail() {
                return "thumbnail";
            }
        };
        ComponentUtil.setFessConfig(mockConfig);

        try {

                    new String[] { fessConfig.getIndexFieldThumbnail(), fessConfig.getIndexFieldConfigId() });
            if (doc == null) {
                throw new ThumbnailGenerationException("Document is not found: " + id);
            }
            final String url = DocumentUtil.getValue(doc, fessConfig.getIndexFieldThumbnail(), String.class);
            if (StringUtil.isBlank(url)) {

            }

            @Override
            public String getIndexFieldUrl() {
                return "url";
            }

            @Override
            public String getIndexFieldThumbnail() {
                return "thumbnail";
            }

            @Override
            public String getIndexFieldClickCount() {
                return "click_count";
            }

            public String getIndexFieldDigest() {
                return baseConfig.getIndexFieldDigest();
            }

            @Override
            public String getIndexFieldThumbnail() {
                return baseConfig.getIndexFieldThumbnail();
            }

            @Override
            public String getIndexFieldClickCount() {
                return baseConfig.getIndexFieldClickCount();
            }

            }

            @Override
            public String getIndexFieldDigest() {
                return "digest";
            }

            @Override
            public String getIndexFieldThumbnail() {
                return "thumbnail";
            }

            @Override
            public String getIndexFieldClickCount() {
                return "click_count";
            }

            }

            @Override
            public String getIndexFieldUrl() {
                return "url";
            }

            @Override
            public String getIndexFieldThumbnail() {
                return "thumbnail";
            }

            @Override
            public String getIndexFieldClickCount() {
                return "click_count";
            }

            }

            @Override
            public String getIndexFieldUrl() {
                return "url";
            }

            @Override
            public String getIndexFieldThumbnail() {
                return "thumbnail";
            }

            @Override
            public String getIndexFieldClickCount() {
                return "click_count";
            }

            }

            @Override
            public String getIndexFieldUrl() {
                return "url";
            }

            @Override
            public String getIndexFieldThumbnail() {
                return "thumbnail";
            }

            @Override
            public String getIndexFieldClickCount() {
                return "click_count";
            }

                    fessConfig.getIndexFieldTitle(), //
                    fessConfig.getIndexFieldDigest(), //
                    fessConfig.getIndexFieldUrl(), //
                    fessConfig.getIndexFieldThumbnail(), //
                    fessConfig.getIndexFieldClickCount(), //
                    fessConfig.getIndexFieldFavoriteCount(), //
                    fessConfig.getIndexFieldConfigId(), //

                searchHelper.getDocumentByDocId(form.docId, queryFieldConfig.getResponseFields(), getUserBean()).orElse(null);
        final String url = DocumentUtil.getValue(doc, fessConfig.getIndexFieldThumbnail(), String.class);
        if (StringUtil.isBlank(form.queryId) || StringUtil.isBlank(url) || !thumbnailSupport) {
            // 404
            throw responseManager.new404("Thumbnail for " + form.docId + " is not found.");