Improvements to ERC and bus parsing.

1) Add some nullptr safety to ERC.
2) Allow unconnected flagging on bus/wire entries.
3) Allow commas in bus group definitions.

Fixes https://gitlab.com/kicad/code/kicad/issues/7155

common/project/net_settings.cpp

@@ -459,17 +459,18 @@ bool NET_SETTINGS::ParseBusGroup( wxString aGroup, wxString* aName,
             }
             else
             {
-                if( aMemberList )
+                if( aMemberList && !tmp.IsEmpty() )
                     aMemberList->push_back( EscapeString( tmp, CTX_NETNAME ) );
 
                 return true;
             }
         }
 
-        if( aGroup[i] == ' ' )
+        // Commas aren't strictly legal, but we can be pretty sure what the author had in mind.
+        if( aGroup[i] == ' ' || aGroup[i] == ',' )
         {
-            if( aMemberList )
-                    aMemberList->push_back( EscapeString( tmp, CTX_NETNAME ) );
+            if( aMemberList && !tmp.IsEmpty() )
+                aMemberList->push_back( EscapeString( tmp, CTX_NETNAME ) );
 
             tmp.Clear();
             continue;

eeschema/connection_graph.cpp

@@ -2375,6 +2375,12 @@ bool CONNECTION_GRAPH::ercCheckBusToBusEntryConflicts( const CONNECTION_SUBGRAPH
     SCH_ITEM* bus_wire = nullptr;
     wxString bus_name;
 
+    if( !aSubgraph->m_driver_connection )
+    {
+        // Incomplete bus entry.  Let the unconnected tests handle it.
+        return true;
+    }
+
     for( auto item : aSubgraph->m_items )
     {
         switch( item->Type() )
@@ -2632,7 +2638,7 @@ bool CONNECTION_GRAPH::ercCheckFloatingWires( const CONNECTION_SUBGRAPH* aSubgra
     if( aSubgraph->m_driver )
         return true;
 
-    std::vector<SCH_LINE*> wires;
+    std::vector<SCH_ITEM*> wires;
 
     // We've gotten this far, so we know we have no valid driver.  All we need to do is check
     // for a wire that we can place the error on.
@@ -2640,7 +2646,9 @@ bool CONNECTION_GRAPH::ercCheckFloatingWires( const CONNECTION_SUBGRAPH* aSubgra
     for( SCH_ITEM* item : aSubgraph->m_items )
     {
         if( item->Type() == SCH_LINE_T && item->GetLayer() == LAYER_WIRE )
-            wires.emplace_back( static_cast<SCH_LINE*>( item ) );
+            wires.emplace_back( item );
+        else if( item->Type() == SCH_BUS_WIRE_ENTRY_T )
+            wires.emplace_back( item );
     }
 
     if( !wires.empty() )
@@ -2674,6 +2682,9 @@ bool CONNECTION_GRAPH::ercCheckLabels( const CONNECTION_SUBGRAPH* aSubgraph )
     if( aSubgraph->m_no_connect )
         return true;
 
+    if( !aSubgraph->m_driver_connection )
+        return true;
+
     // Buses are excluded from this test: many users create buses with only a single instance
     // and it's not really a problem as long as the nets in the bus pass ERC
     if( aSubgraph->m_driver_connection->IsBus() )