class PartBase implements Part {

    /**
     * The name of the form field, part of the Content-Disposition header
     */
    private final String name;

    /**
     * The main part of the Content-Type header
     */
    private final String contentType;

    /**
     * The charset (part of Content-Type header)
     */
    private final Charset charset;

    /**
     * The Content-Transfer-Encoding header value.
     */
    private final String transferEncoding;

    /**
     * The Content-Id
     */
    private final String contentId;

    /**
     * The disposition type (part of Content-Disposition)
     */
    private String dispositionType;

    /**
     * Additional part headers
     */
    private List<Param> customHeaders;

    /**
     * Constructor.
     *
     * @param name             The name of the part, or {@code null}
     * @param contentType      The content type, or {@code null}
     * @param charset          The character encoding, or {@code null}
     * @param contentId        The content id, or {@code null}
     * @param transferEncoding The transfer encoding, or {@code null}
     */
    protected PartBase(String name, String contentType, Charset charset, String contentId, String transferEncoding) {
        this.name = name;
        this.contentType = contentType;
        this.charset = charset;
        this.contentId = contentId;
        this.transferEncoding = transferEncoding;
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public String getContentType() {
        return contentType;
    }

    @Override
    public Charset getCharset() {
        return charset;
    }

    @Override
    public String getTransferEncoding() {
        return transferEncoding;
    }

    @Override
    public String getContentId() {
        return contentId;
    }

    @Override
    public String getDispositionType() {
        return dispositionType;
    }

    public void setDispositionType(String dispositionType) {
        this.dispositionType = dispositionType;
    }

    @Override
    public List<Param> getCustomHeaders() {
        return customHeaders;
    }

    public void setCustomHeaders(List<Param> customHeaders) {
        this.customHeaders = customHeaders;
    }

    public void addCustomHeader(String name, String value) {<FILL_FUNCTION_BODY>}

    @Override
    public String toString() {
        return getClass().getSimpleName() +
                " name=" + getName() +
                " contentType=" + getContentType() +
                " charset=" + getCharset() +
                " transferEncoding=" + getTransferEncoding() +
                " contentId=" + getContentId() +
                " dispositionType=" + getDispositionType();
    }
}

        if (customHeaders == null) {
            customHeaders = new ArrayList<>(2);
        }
        customHeaders.add(new Param(name, value));
    
<no_super_class>