LO:MailMerge supplying OutServerPassword via macro

I've got some code that uses MailMerge to email documents. It works. However, the password is stored in registrymodifications.xcu in clear text.

Trying to move forward

I cleared the password from registrymodifications.xcu by

Tools -> Options -> LibreOffice Writer -> Mail Merge E-mail -> Server Authentication

and deleting the contents of the password field.

The line in registrymodifications

changed from

<item oor:path="/org.openoffice.Office.Writer/MailMergeWizard"><prop oor:name="MailPassword" oor:op="fuse"><value>XXXXXXX YYYYYYY</value></prop></item>

to

<item oor:path="/org.openoffice.Office.Writer/MailMergeWizard"><prop oor:name="MailPassword" oor:op="fuse"><value></value></prop></item>

I then changed my macro to include the MailMerge property OutServerPassword. As in the code snippet below

oMailMerge = CreateUnoService("com.sun.star.text.MailMerge")
    oMailMerge.DocumentURL =  ConvertToUrl(strSelectedTemplate)
    oMailMerge.DataSourceName =  "MySQLDataBase"
    oMailMerge.CommandType = 0        'Command

oMailMerge.Command = "MySQLDataBase.tbl_temporary"
    oMailMerge.OutputType = com.sun.star.text.MailMergeType.MAIL
    oMailMerge.Subject = strTitle
    oMailMerge.AddressFromColumn = "Email_Address"
    oMailMerge.OutServerPassword="XXXXXXX YYYYYYY"

oMailMerge.SendAsHTML = True

oMailMerge.execute(Array())

When I run the script it fails with the following error message box

BASIC runtime error.
An exception occurred
Type: com.sun.star.uno.Exception
Message: Mail merge failed. Sorry, no further information available..

What am I doing wrong?

Has anyone else got this working?