QGIS » QGIS Application

I am using the following code to load a vector layer from a PostGIS table:

uri = QgsDataSourceURI()
uri.setConnection(self.host, str(self.port), self.database, self.username, self.password)
uri.setDataSource(schema, postGisTable, "the_geom",sqlstmt,'gid')
try:
    #if sql does not return data - get PostGIS error, but not exception?
    vlayer = QgsVectorLayer(uri.uri(), layerName, "postgres")
except:
    QMessageBox.critical(self.iface.mainWindow(), "Error", "Problem setting QgsVectorLayer")
if not vlayer.isValid():
    QMessageBox.critical(self.iface.mainWindow(),"Error","Layer failed to load!")

If the sqlstmt returns an empty query, in some cases my plugin shows the "Layer failed to load!" message meaning the layer is invalid (but is never caught by the previous try block).
Error in the General Log Messages is:

Geometry type and srid for empty column the_geom of "cmt"."subbasinsoilsdrainage_eastern_union" undefined.

On investigation I have discovered that if the Geometry type of the PostGIS layer is the generic GEOMETRY type, then I get this error. If the Geometry type is MultiPolygon or MultiPoint, then an empty layer works OK.

If this is expected behaviour then should we avoid the GEOMETRY type in our PostGIS tables?