Fix crossfade undo using the stateful diff system. Fixes #3257.

git-svn-id: svn://localhost/ardour2/branches/3.0@7694 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 4 insertions, 0 deletions

diff --git a/libs/pbd/pbd/command.h b/libs/pbd/pbd/command.h
index c6c3c8d3fd..db4d2bbd81 100644
--- a/libs/pbd/pbd/command.h
+++ b/libs/pbd/pbd/command.h
@@ -43,6 +43,10 @@ public:
 	virtual XMLNode &get_state();
 	virtual int set_state(const XMLNode&, int /*version*/) { /* noop */ return 0; }
 
+	virtual bool empty () const {
+		return false;
+	}
+
 protected:
 	Command() {}
 	Command(const std::string& name) : _name(name) {}