in src/main/java/com/spotify/google/cloud/pubsub/client/Pubsub.java [1009:1013]
public Builder compressionLevel(final int compressionLevel) {
checkArgument(compressionLevel > -1 && compressionLevel <= 9, "compressionLevel must be -1 or 0-9.");
this.compressionLevel = compressionLevel;
return this;
}