@Override
	protected void actionPerformed(SymbolTreeActionContext context) {

		LocationReferencesService locationReferencesService =
			tool.getService(LocationReferencesService.class);

		CodeViewerService codeViewerService = tool.getService(CodeViewerService.class);
		Navigatable navigatable = codeViewerService.getNavigatable();

		TreePath[] selectionPaths = context.getSelectedSymbolTreePaths();
		SymbolNode symbolNode = (SymbolNode) selectionPaths[0].getLastPathComponent();
		ProgramLocation location = getProgramLocation(symbolNode);
		if (location == null) {
			Msg.debug(this, "Do not know how to show references to SymbolNode type: " + symbolNode);
			return;
		}

		locationReferencesService.showReferencesToLocation(location, navigatable);
	}
We need this when our plugin is loaded before the service we are using
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/symboltree/actions/ShowSymbolReferencesAction.java