explicit inspect for null instead of fail because of a NPE (#876)

Signed-off-by: Markus Rathgeb <maggu2810@gmail.com>

itests/org.openhab.core.tests/src/main/java/org/eclipse/smarthome/core/types/util/UnitUtilsTest.java

@@ -60,9 +60,11 @@ public class UnitUtilsTest {
     @Test
     public void whenValidDimensionIsGiven_shouldCreateQuantityClass() {
         Class<? extends Quantity<?>> temperature = UnitUtils.parseDimension("Temperature");
+        assertNotNull(temperature);
         assertTrue(Temperature.class.isAssignableFrom(temperature));
 
         Class<? extends Quantity<?>> intensity = UnitUtils.parseDimension("Intensity");
+        assertNotNull(intensity);
         assertTrue(Intensity.class.isAssignableFrom(intensity));
     }