CMIS Custom property

Hi,

i try to add a custom property to a cmis document. The default properties ,like OBJECT_TYPE_ID or NAME, are defined in the PropertyID.class. How can I add a custom property? I tried to simply put a String "my:int.property and a value "42" in the hash map but I've got the exception:

errorMessage":"Property 'my:int.property' is not valid for this type or one of the secondary types!

private Map<String, Object> createCmisDocumentProperties(final AttachmentRef attachment)

    {

        // properties for the document to store.

        final Map<String, Object> documentProps = new HashMap<String, Object>();

        documentProps.put(PropertyIds.OBJECT_TYPE_ID, "cmis:document");

        documentProps.put(PropertyIds.NAME, FilenameUtils.getName(attachment.getName()));

        documentProps.put(PropertyIds.CONTENT_STREAM_FILE_NAME, FilenameUtils.getName(attachment.getName()));

        documentProps.put(PropertyIds.CONTENT_STREAM_LENGTH, attachment.getFileSize());

        documentProps.put(PropertyIds.CONTENT_STREAM_MIME_TYPE, attachment.getMimeType());

      documentProps.put("my:int.property", 42);

        return documentProps;

    }

Thanks for helping me.