fix(datastore): Handling nil slices in save and query (#8043)

* fix(datastore): Handling nil slices in save and query

* fix(datastore): Handling nil slices in save & query

datastore/load.go

@@ -161,6 +161,11 @@ func (l *propertyLoader) loadOneElement(codec fields.List, structValue reflect.V
 			structValue = v
 		}
 
+		if v.Kind() == reflect.Slice && p.Value == nil {
+			v.Set(reflect.Zero(v.Type()))
+			return ""
+		}
+
 		// If the element is a slice, we need to accommodate it.
 		if v.Kind() == reflect.Slice && v.Type() != typeOfByteSlice {
 			if l.m == nil {

datastore/load_test.go

@@ -316,6 +316,18 @@ func TestLoadEntityNested(t *testing.T) {
 				A: []Simple{{I: 3}, {I: 4}},
 			},
 		},
+		{
+			desc: "nested simple with nil slice",
+			src: &pb.Entity{
+				Properties: map[string]*pb.Value{
+					"A": {ValueType: &pb.Value_NullValue{}},
+				},
+			},
+
+			want: &NestedSliceOfSimple{
+				A: nil,
+			},
+		},
 		{
 			desc: "nested with multiple anonymous fields",
 			src: &pb.Entity{

datastore/save.go

@@ -265,6 +265,11 @@ func (s structPLS) key(v reflect.Value) (*Key, error) {
 func saveSliceProperty(props *[]Property, name string, opts saveOpts, v reflect.Value) error {
 	// Easy case: if the slice is empty, we're done.
 	if v.Len() == 0 {
+		*props = append(*props, Property{
+			Name:    name,
+			Value:   nil,
+			NoIndex: opts.noIndex,
+		})
 		return nil
 	}
 	// Work out the properties generated by the first element in the slice. This will