In version 4.4 of sitefinity we are using the following filter expression in the download list
Visible = true AND Status = Live AND (ourCustomField = null OR ourCustomField= false)
where ourCustomField is a custom boolean field.
This all works fine in 4.4, however in version 5 the ourCustomField = null expression generates a cannot parse template exception, it is ok with the ourCustomField = false. How can you test for a null value in version 5 filter expressions without generating a cannot parse template error?