def _ensureData(self, data):
        """Check data validity"""
        if data is None:
            data = self.fw.dataVals

        vals = self.checkData(data)

        if vals is None:
            pg.critical("There are no data values.")

        if abs(min(vals)) < 1e-12:
            print(min(vals), max(vals))
            pg.critical("There are zero data values.")

        return vals