Allowing PCell layer parameters without default (-> empty)

src/db/db/built-in-macros/pcell_declaration_helper.lym

@@ -408,7 +408,7 @@ module RBA
     
     # get the layer definitions
     def get_layers(parameters)
-      @layer_param_index.collect { |i| parameters[i] }
+      @layer_param_index.collect { |i| parameters[i] || RBA::LayerInfo::new }
     end
       
     # coerce parameters (make consistent)

src/db/db/built-in-pymacros/pcell_declaration_helper.lym

@@ -430,7 +430,10 @@ class _PCellDeclarationHelper(pya.PCellDeclaration):
     """
     layers = []
     for i in self._layer_param_index:
-      layers.append(parameters[i])
+      if parameters[i] is not None:
+        layers.append(parameters[i])
+      else:
+        layers.append(pya.LayerInfo())
     return layers
     
   def callback(self, layout, name, states):

src/db/db/gsiDeclDbLibrary.cc

@@ -263,7 +263,7 @@ static std::vector<db::LayerProperties> get_layer_declarations_native (const db:
   std::vector<db::PCellLayerDeclaration> lp = pd->db::PCellDeclaration::get_layer_declarations (parameters);
   std::vector<db::LayerProperties> ret;
   for (std::vector<db::PCellLayerDeclaration>::const_iterator l = lp.begin (); l != lp.end (); ++l) {
-    ret.push_back (db::LayerProperties(*l));
+    ret.push_back (db::LayerProperties (*l));
   }
   return ret;
 }