@Anonymous
According to https://msdn.microsoft.com/en-us/library/azure/mt643789.aspx you can use this expression in a condition block to handle null trigger outputs
@coalesce(trigger().outputs?.body?.property1, 'my default value')
I implemented a test flow with a New Sharepoint item trigger, the following condition
@equals(coalesce(trigger().outputs?.body?.propertyX, 'NULL'), 'NULL')
On the YES branch I included a "Send email" action block for confirmation purposes, leaving the NO branch empty.
In the Sharepoint list definition I included an optional column (propertyX), then I added an iten without filling the optional column.
The flow succeded and I received the confirmation email. But when opening again the flow for editing purposes the following error is displayed:
"unexpected character '?', mode 3"
and no flow block is displayed anymore.
Assuming this is the way to proceed, It will be more user frienly if the condition block offers an option called "not present" and internally converts it to the above expression