@Nullable
    @Override
    public MediaType contentType() {
        final MediaType contentType = (MediaType) cache.get(HttpHeaderNames.CONTENT_TYPE);
        if (contentType != null) {
            return contentType;
        }

        final String contentTypeString = get(HttpHeaderNames.CONTENT_TYPE);
        if (contentTypeString == null) {
            return null;
        }

        try {
            final MediaType parsed = MediaType.parse(contentTypeString);
            cache.put(HttpHeaderNames.CONTENT_TYPE, parsed);
            return parsed;
        } catch (IllegalArgumentException unused) {
            // Invalid media type
            return null;
        }
    }
Adds the specified {@code setCookies} with {@link HttpHeaderNames#SET_COOKIE}.
core/src/main/java/com/linecorp/armeria/common/HttpHeadersBase.java