[ui] By default no pipeline is provided and we can create empty project

meshroom/ui/reconstruction.py

@@ -510,6 +510,8 @@ class Reconstruction(UIGraph):
     @Slot(str)
     def new(self, pipeline=None):
         p = pipeline if pipeline != None else self._defaultPipeline
+        if not p:
+            return
         """ Create a new pipeline. """
         # Lower the input and the dictionary keys to make sure that all input types can be found:
         # - correct pipeline name but the case does not match (e.g. panoramaHDR instead of panoramaHdr)