private File decompressApplication(InputStream in, String contentType, File tempDir) {
        try (CompressedApplicationInputStream application =
                     CompressedApplicationInputStream.createFromCompressedStream(in, contentType, configserverConfig.maxApplicationPackageSize())) {
            return decompressApplication(application, tempDir);
        } catch (IOException e) {
            throw new IllegalArgumentException("Unable to decompress data in body", e);
        }
    }
Gets the active Session for the given application id.

@return the active session, or null if there is no active session for the given application id.
configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java