Does every row in a gridImageColumn have to show an image?

I need to display a set of records in a grid. I'm using a!gridField. One of the columns will be a!gridImageColumn and its presenting a bit of a challenge. For this column when the value is true then it should display "STATUS_OK" when false it should be blank. Unfortunately I must return an image. I'm forced to use something like an unobtrusive "REMOVE_DISABLED" icon as a workaround

Even replacing the if statement with something like this fails:  a!documentImage(document: a!iconIndicator(icon: "STATUS_OK"), showWhen: fv!item).

Anytime there is no image or showWhen = false, I get the message below. ie. Must be SafeImage or DocumentImage.

An Error Has Occurred Expression evaluation error [evaluation ID = BJKF4MAN] in rule 'mr_tam_sc_newassignmentsearch' (called by rule 'mr_tam_if_assignmentdashboard') at function a!gridField [line 22]: The image at index Include Approvals of an grid [label=“”] has an invalid value for “data”. “data” must be of the type SafeImage or DocumentImage. (APNX-1-4255-002)

This may be as good as it gets but before I give up I thought I'd ask. 

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