[vala/0.40] codegen: Use CCodeInvalidExpression instead of place holders

[Rico Tzschichholz <ricotz src gnome org>]

commit 43df311d7bc4978614af44b65dcd2dfc73c223f7
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Wed Dec 30 14:50:05 2020 +0100

    codegen: Use CCodeInvalidExpression instead of place holders

 codegen/valaccodebasemodule.vala | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/codegen/valaccodebasemodule.vala b/codegen/valaccodebasemodule.vala
index b87cf2974..0199ebba4 100644
--- a/codegen/valaccodebasemodule.vala
+++ b/codegen/valaccodebasemodule.vala
@@ -6554,15 +6554,15 @@ public abstract class Vala.CCodeBaseModule : CodeGenerator {
        }
 
        public virtual CCodeExpression get_param_spec_cexpression (Property prop) {
-               return new CCodeFunctionCall (new CCodeIdentifier (""));
+               return new CCodeInvalidExpression ();
        }
 
        public virtual CCodeExpression get_param_spec (Property prop) {
-               return new CCodeFunctionCall (new CCodeIdentifier (""));
+               return new CCodeInvalidExpression ();
        }
 
        public virtual CCodeExpression get_signal_creation (Signal sig, TypeSymbol type) {
-               return new CCodeFunctionCall (new CCodeIdentifier (""));
+               return new CCodeInvalidExpression ();
        }
 
        public virtual void register_dbus_info (CCodeBlock block, ObjectTypeSymbol bindable) {
@@ -6603,7 +6603,7 @@ public abstract class Vala.CCodeBaseModule : CodeGenerator {
        }
 
        public virtual CCodeExpression get_array_length_cexpression (Expression array_expr, int dim = -1) {
-               return new CCodeConstant ("");
+               return new CCodeInvalidExpression ();
        }
 
        public virtual CCodeExpression get_array_length_cvalue (TargetValue value, int dim = -1) {