NPE if "null" layout is set

[ptziegler]

This can happen with e.g.

contentPanel.setLayout(null);
contentPanel.setLayout(new GridBagLayout());

Because it's not allowed to set multiple layouts, an error message is created. This message contains the name of the old and new layout, but doesn't handle the case where one is "null".

java.lang.NullPointerException: Cannot invoke "java.lang.Class.getName()" because the return value of "org.eclipse.wb.internal.core.model.description.ComponentDescription.getComponentClass()" is null
	at org.eclipse.wb.internal.swing.model.component.ContainerInfo.lambda$0(ContainerInfo.java:118)
	at org.eclipse.wb.internal.core.model.layout.AbstractLayoutInfo.lambda$0(AbstractLayoutInfo.java:106)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:565)
	at org.eclipse.wb.internal.core.utils.reflect.ReflectionUtils.invokeMethod(ReflectionUtils.java:915)
	at org.eclipse.wb.core.model.broadcast.BroadcastSupport.lambda$0(BroadcastSupport.java:213)
	at org.eclipse.wb.core.model.broadcast.ObjectInfoChildAddBefore$ByteBuddy$NCEm66Hs.invoke(Unknown Source)
	at org.eclipse.wb.core.model.ObjectInfo.addChild(ObjectInfo.java:200)
	at org.eclipse.wb.core.model.ObjectInfo.addChild(ObjectInfo.java:166)
	at org.eclipse.wb.internal.swing.model.component.ContainerInfo.addExplicitAbsoluteLayoutChild(ContainerInfo.java:388)
	at org.eclipse.wb.internal.swing.model.component.ContainerInfo.initialize_createAbsoluteLayout(ContainerInfo.java:376)
	at org.eclipse.wb.internal.swing.model.component.ContainerInfo$1.invoke(ContainerInfo.java:134)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:565)