fx: handle nullptr arguments in all iterator functions

fx/iterator.c

@@ -25,6 +25,10 @@ static enum fx_status iterator_set_status(
 
 const fx_iterator *fx_iterator_begin(const fx_iterable *it)
 {
+	if (!it) {
+		return NULL;
+	}
+
 	FX_CLASS_DISPATCH_VIRTUAL_0(
 		fx_iterable,
 		FX_TYPE_ITERABLE,
@@ -35,11 +39,19 @@ const fx_iterator *fx_iterator_begin(const fx_iterable *it)
 
 enum fx_status fx_iterator_get_status(const fx_iterator *it)
 {
+	if (!it) {
+		return FX_ERR_NO_DATA;
+	}
+
 	FX_CLASS_DISPATCH_STATIC_0(FX_TYPE_ITERATOR, iterator_get_status, it);
 }
 
 enum fx_status fx_iterator_set_status(const fx_iterator *it, fx_status status)
 {
+	if (!it) {
+		return FX_ERR_NO_DATA;
+	}
+
 	FX_CLASS_DISPATCH_STATIC(
 		FX_TYPE_ITERATOR,
 		iterator_set_status,
@@ -49,11 +61,14 @@ enum fx_status fx_iterator_set_status(const fx_iterator *it, fx_status status)
 
 enum fx_status fx_iterator_move_next(const fx_iterator *it)
 {
+	if (!it) {
+		return FX_ERR_NO_DATA;
+	}
+
 	enum fx_status status = FX_ERR_NOT_SUPPORTED;
 
-	fx_iterator_class *iface = fx_object_get_interface(
+	fx_iterator_class *iface
-		it,
+		= fx_object_get_interface(it, FX_TYPE_ITERATOR);
-		FX_TYPE_ITERATOR);
 	if (iface && iface->it_move_next) {
 		status = iface->it_move_next(it);
 	}
@@ -66,6 +81,10 @@ enum fx_status fx_iterator_move_next(const fx_iterator *it)
 
 const fx_value *fx_iterator_get_value(const fx_iterator *it)
 {
+	if (!it) {
+		return NULL;
+	}
+
 	FX_CLASS_DISPATCH_VIRTUAL_0(
 		fx_iterator,
 		FX_TYPE_ITERATOR,
@@ -76,11 +95,14 @@ const fx_value *fx_iterator_get_value(const fx_iterator *it)
 
 fx_status fx_iterator_erase(fx_iterator *it)
 {
+	if (!it) {
+		return FX_ERR_NO_DATA;
+	}
+
 	enum fx_status status = FX_ERR_NOT_SUPPORTED;
 
-	fx_iterator_class *iface = fx_object_get_interface(
+	fx_iterator_class *iface
-		it,
+		= fx_object_get_interface(it, FX_TYPE_ITERATOR);
-		FX_TYPE_ITERATOR);
 	if (iface && iface->it_erase) {
 		status = iface->it_erase(it);
 	}