assume obj is non-nil in obfuscatedObjectName

Only two callers did pass nil, and there's no reason for them to do so.
They should be the ones to check that typeToObj did not return nil.

reflect.go

@@ -189,13 +189,13 @@ func (ri *reflectInspector) checkFunction(fun *ssa.Function) {
 			switch inst := inst.(type) {
 			case *ssa.Store:
 				obj := typeToObj(inst.Addr.Type())
-				if usedForReflect(ri.result, obj) {
+				if obj != nil && usedForReflect(ri.result, obj) {
 					ri.recordArgReflected(inst.Val, make(map[ssa.Value]bool))
 					ri.propagatedInstr[inst] = true
 				}
 			case *ssa.ChangeType:
 				obj := typeToObj(inst.X.Type())
-				if usedForReflect(ri.result, obj) {
+				if obj != nil && usedForReflect(ri.result, obj) {
 					ri.recursivelyRecordUsedForReflect(inst.Type(), nil)
 					ri.propagatedInstr[inst] = true
 				}
@@ -467,12 +467,9 @@ func recordedObjectString(obj types.Object) objectString {
 // obfuscatedObjectName returns the obfucated name of a types.Object,
 // parent is needed to correctly get the obfucated name of struct fields
 func obfuscatedObjectName(obj types.Object, parent *types.Struct) string {
-	if obj == nil {
-		return ""
-	}
 	pkg := obj.Pkg()
 	if pkg == nil {
-		return ""
+		return "" // builtin types are never obfuscated
 	}
 
 	if v, ok := obj.(*types.Var); ok && parent != nil {