Fix box-shadow output
Fix box-shadow output

Seems like length for a null value returns ‘1’ instead of 0. Using a
null check instead.

Change-Id: Ia7fc7479b49c40bcef791c303e88699735bf6019

shahrzadmn/vaadin-grid,manolo/components,shahrzadmn/vaadin-grid,jforge/components,manolo/components,jforge/components,shahrzadmn/vaadin-grid,manolo/components,shahrzadmn/vaadin-grid,jforge/components