allow for null ViewportAxisListener
diff --git a/org.eclipse.nebula.widgets.nattable.core.test/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxisTest.xtend b/org.eclipse.nebula.widgets.nattable.core.test/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxisTest.xtend
index 6fb8028..c3a7bc2 100644
--- a/org.eclipse.nebula.widgets.nattable.core.test/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxisTest.xtend
+++ b/org.eclipse.nebula.widgets.nattable.core.test/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxisTest.xtend
@@ -21,7 +21,7 @@
 			setPixelSizeOfSegmentPosition(7, 2)
 			setPixelSizeOfSegmentPosition(13, 3)
 		]
-		viewportAxis = new ViewportAxis(underlyingAxis, [| /* do nothing */])
+		viewportAxis = new ViewportAxis(underlyingAxis, null)
 	}
 	
 	@Test
diff --git a/org.eclipse.nebula.widgets.nattable.core/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxis.xtend b/org.eclipse.nebula.widgets.nattable.core/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxis.xtend
index aa3d35f..edaa6ae 100644
--- a/org.eclipse.nebula.widgets.nattable.core/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxis.xtend
+++ b/org.eclipse.nebula.widgets.nattable.core/src/org/eclipse/nebula/widgets/nattable/core/layer/impl/viewport/ViewportAxis.xtend
@@ -39,7 +39,7 @@
 	
 	def void setPixelOrigin(int pixelOrigin) {
 		this.pixelOrigin = pixelOrigin
-		viewportAxisListener.viewportAxisChanged
+		viewportAxisListener?.viewportAxisChanged
 	}
 	
 	def int getOriginSegmentPosition() {