Arch: Small bugfix in IFC exporter

src/Mod/Arch/importIFC.py

@@ -1520,7 +1520,10 @@ class recycler:
             return c
 
     def createIfcSurfaceStyle(self,name,r,g,b):
-        key = name+str((r,g,b))
+        if name:
+            key = name + str((r,g,b))
+        else:
+            key = str((r,g,b))
         if self.compress and key in self.sstyles:
             self.spared += 1
             return self.sstyles[key]
@@ -1533,7 +1536,10 @@ class recycler:
             return c
 
     def createIfcPresentationStyleAssignment(self,name,r,g,b):
-        key = name+str((r,g,b))
+        if name:
+            key = name+str((r,g,b))
+        else:
+            key = str((r,g,b))
         if self.compress and key in self.psas:
             self.spared += 1
             return self.psas[key]