WCPS - proper error message when axis iterator of coverage constructor is string

[Bang Pham Huu]

This query has date time as string

for $c in (test_eobstest) 
return 
encode(
coverage result
over $y lat  (-90 : -85),
     $x long  (-180 : -170),
     $t t ("2015-01-01T00:00:00.000Z":"2018-01-01T00:00:00.000Z")
values $c[ Lat($y), Long($x), t($t)]
,
"csv"
)

it should have proper error like

Please specify integer grid coordinates, or use the imageCrsDomain
function to derive them automatically from geo coordinates for 
coverage constructor "result", iterator variable $i.