explicitFileType = Optional.fromNullable(fileType);
        lastKnownFileType = Optional.absent();
    }

    public Optional<String> getExplicitFileType() {
        return explicitFileType;
    }

    public void setExplicitFileType(Optional<String> explicitFileType) {
        this.explicitFileType = explicitFileType;
    }

    @Override
    public String isa() {