Make default link controller pass actual start location, not null

The default link controller in ControllerBase would invoke link
with argument startLocation being null rather than the start location.

Issue-Ref: 3924
Issue-Url: https://af3-developer.fortiss.org/issues/3924


Signed-off-by: Ulrich Schöpp <schoepp@fortiss.org>

org.fortiss.tooling.common.ui/src/org/fortiss/tooling/common/ui/javafx/lwfxef/controller/base/.ratings

 AnchorageContentControllerBase.java da56b10cbf2711b5da69f0b59f43eacbe54f4eea YELLOW
 ClickControllerBase.java 8e5861ed5f9318008ad0fdd5497ed320cd5bd647 YELLOW
 ContentAnchorageMoveControllerBase.java c18e7915ce23e124757f5b736086ecc46694800a YELLOW
-ControllerBase.java 309e9ee3f3a255b5a06fed8f1b4d4ec8bf88f101 YELLOW
+ControllerBase.java 6f32c252fad45327c5ece55ec81f517421d2d4a6 YELLOW
 DefaultDiagramController.java 0e083b89a08f63967102a384d66ebc1d64d203af YELLOW
 DelegatingContentAnchorageController.java 2e3b1b4e14402a3503233f816b21ef3e4aa09edc YELLOW
 DragControllerBase.java b15ff874304f679fe494d85f57cc8cbe4d0d1d15 YELLOW

org.fortiss.tooling.common.ui/src/org/fortiss/tooling/common/ui/javafx/lwfxef/controller/base/ControllerBase.java

@@ -147,7 +147,13 @@ public abstract class ControllerBase extends MVCBundlePartBase implements IContr
 			IMVCBundle startBundle = getMVCBundle();
 			getViewer().terminateNewLinkLineFeedback();
 			if(canLink(startBundle, startDiagramLocation, endBundle, endDiagramLocation)) {
-				return () -> link(startBundle, startDiagramLocation, endBundle, endDiagramLocation);
+				// Need to copy the location to a local variable to make sure that it is passed
+				// by value to the returned closure. Otherwise the closure will capture 'this' and
+				// link will see a future value of startDiagramLocation, likely null because
+				// startDiagramLocation is being set to null right after this return.
+				final DiagramCoordinate startDiagramLocation_ = startDiagramLocation;
+				return () -> link(startBundle, startDiagramLocation_, endBundle,
+						endDiagramLocation);
 			}
 			return null;
 		}