NULL ignore in {model.value}

I have hit a problem with CC5. A connection that i have used for many months now.
I use [pre]<td class='tdPhone njjoCenter'>{mdlListMembership.phone}</td>
[/pre]to display a phone number which may be NULL. That has worked fine leaving an empty field.

Early this week - just after running the latest CF6 and CC6 upgrades those NULL fields began to display as (literally)

{mdlListMembership.phone}

I had to change the code to[br]

<td class='tdPhone njjoCenter'><?php echo $phones->memberPhone;?></td>

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Similar code written in CF6 does not show that problem.
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Regards
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Nick