public MultipartEntityBuilder addParameter(final BasicNameValuePair parameter) {
        this.contentType = contentType.withParameters(parameter);
        return this;
    }
Add parameter to the current {@link ContentType}.

@param parameter The name-value pair parameter to add to the {@link ContentType}.
@return this instance.
@since 5.2
httpclient5/src/main/java/org/apache/hc/client5/http/entity/mime/MultipartEntityBuilder.java