Add NIL_IS_VARIANT usage to few definitions

The missing usage flag led to GDNative API descriptions containting
arguments with "void" type.

modules/gdscript/gd_function.cpp

@@ -1578,7 +1578,7 @@ void GDFunctionState::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("is_valid", "extended_check"), &GDFunctionState::is_valid, DEFVAL(false));
 	ClassDB::bind_vararg_method(METHOD_FLAGS_DEFAULT, "_signal_callback", &GDFunctionState::_signal_callback, MethodInfo("_signal_callback"));
 
-	ADD_SIGNAL(MethodInfo("completed", PropertyInfo(Variant::NIL, "result")));
+	ADD_SIGNAL(MethodInfo("completed", PropertyInfo(Variant::NIL, "result", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NIL_IS_VARIANT)));
 }
 
 GDFunctionState::GDFunctionState() {

modules/visual_script/visual_script_nodes.cpp

@@ -1109,7 +1109,7 @@ void VisualScriptConstant::_bind_methods() {
 	}
 
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "type", PROPERTY_HINT_ENUM, argt), "set_constant_type", "get_constant_type");
-	ADD_PROPERTY(PropertyInfo(Variant::NIL, "value"), "set_constant_value", "get_constant_value");
+	ADD_PROPERTY(PropertyInfo(Variant::NIL, "value", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NIL_IS_VARIANT), "set_constant_value", "get_constant_value");
 }
 
 class VisualScriptNodeInstanceConstant : public VisualScriptNodeInstance {

scene/gui/rich_text_label.cpp

@@ -1949,7 +1949,7 @@ void RichTextLabel::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "visible_characters", PROPERTY_HINT_RANGE, "-1,128000,1"), "set_visible_characters", "get_visible_characters");
 	ADD_PROPERTY(PropertyInfo(Variant::REAL, "percent_visible", PROPERTY_HINT_RANGE, "0,1,0.001"), "set_percent_visible", "get_percent_visible");
 
-	ADD_SIGNAL(MethodInfo("meta_clicked", PropertyInfo(Variant::NIL, "meta")));
+	ADD_SIGNAL(MethodInfo("meta_clicked", PropertyInfo(Variant::NIL, "meta", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NIL_IS_VARIANT)));
 
 	BIND_ENUM_CONSTANT(ALIGN_LEFT);
 	BIND_ENUM_CONSTANT(ALIGN_CENTER);