Added IsNil function to assert to Object or ItemCollection before checking for nil values in Item interface

collection.go

@@ -314,7 +314,7 @@ func (c Collection) ItemsMatch(col ...Item) bool {
 
 // Equals
 func (c Collection) Equals(with Item) bool {
-	if with == nil {
+	if IsNil(with) {
 		return false
 	}
 	if !with.IsCollection() {

collection_page.go

@@ -308,7 +308,7 @@ func (c CollectionPage) ItemsMatch(col ...Item) bool {
 
 // Equals
 func (c CollectionPage) Equals(with Item) bool {
-	if with == nil {
+	if IsNil(with) {
 		return false
 	}
 	if !with.IsCollection() {

decoding.go

@@ -171,7 +171,7 @@ func itemFn(data []byte) (Item, error) {
 		}
 	}
 	i, err := ItemTyperFunc(typ)
-	if err != nil || i == nil {
+	if err != nil || IsNil(i) {
 		return nil, nil
 	}
 

encoding.go

@@ -97,7 +97,7 @@ func writeIRIProp(b *[]byte, n string, i LinkOrIRI) (notEmpty bool) {
 }
 
 func writeItemProp(b *[]byte, n string, i Item) (notEmpty bool) {
-	if i == nil {
+	if IsNil(i) {
 		return notEmpty
 	}
 	if im, ok := i.(json.Marshaler); ok {

helpers.go

@@ -314,8 +314,9 @@ func notEmptyActor(a *Actor) bool {
 		len(a.PublicKey.PublicKeyPem) > 0)
 }
 
+// NotEmpty
 func NotEmpty(i Item) bool {
-	if i == nil {
+	if IsNil(i) {
 		return false
 	}
 	var notEmpty bool

item.go

@@ -13,7 +13,7 @@ const (
 
 // ItemsEqual checks if it and with Items are equal
 func ItemsEqual(it, with Item) bool {
-	if it == nil || with == nil{
+	if IsNil(it) || IsNil(with) {
 		return with == it
 	}
 	result := true
@@ -76,7 +76,8 @@ func ItemsEqual(it, with Item) bool {
 // IsItemCollection returns if the current Item interface holds a Collection
 func IsItemCollection(it Item) bool {
 	_, ok := it.(ItemCollection)
-	return ok
+	_, okP := it.(*ItemCollection)
+	return ok || okP
 }
 
 // IsIRI returns if the current Item interface holds an IRI
@@ -94,3 +95,24 @@ func IsObject(it Item) bool {
 	}
 	return ok
 }
+
+// IsNil checks if the object matching an ObjectOrLink interface is nil
+func IsNil(it Item) bool {
+	if it == nil {
+		return true
+	}
+	// This is the default if the argument can't be casted to Object, as is the case for an ItemCollection
+	isNil := false
+	if IsItemCollection(it) {
+		OnItemCollection(it, func(c *ItemCollection) error {
+			isNil = c == nil
+			return nil
+		})
+	} else {
+		OnObject(it, func(o *Object) error {
+			isNil = o == nil
+			return nil
+		})
+	}
+	return isNil
+}

item_collection.go

@@ -198,7 +198,7 @@ func (i ItemCollection) ItemsMatch(col ...Item) bool {
 
 // Equals
 func (i ItemCollection) Equals(with Item) bool {
-	if with == nil {
+	if IsNil(with) {
 		return false
 	}
 	if !with.IsCollection() {

item_test.go

@@ -80,3 +80,112 @@ func TestItemsEqual(t *testing.T) {
 		})
 	}
 }
+
+func TestIsNil(t *testing.T) {
+	type args struct {
+		it Item
+	}
+	var (
+		o      *Object
+		col    *ItemCollection
+		obNil  Item = o
+		colNil Item = col
+	)
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			name: "plain-nil",
+			args: args{
+				it: nil,
+			},
+			want: true,
+		},
+		{
+			name: "interface-nil",
+			args: args{
+				it: Item(nil),
+			},
+			want: true,
+		},
+		{
+			name: "object-nil",
+			args: args{
+				it: obNil,
+			},
+			want: true,
+		},
+		{
+			name: "collection-nil",
+			args: args{
+				it: colNil,
+			},
+			want: true,
+		},
+		{
+			name: "collection-not-nil",
+			args: args{
+				it: ItemCollection{},
+			},
+			want: false,
+		},
+		{
+			name: "object-not-nil",
+			args: args{
+				it: &Object{},
+			},
+			want: false,
+		},
+		{
+			name: "place-not-nil",
+			args: args{
+				it: &Place{},
+			},
+			want: false,
+		},
+		{
+			name: "tombstone-not-nil",
+			args: args{
+				it: &Tombstone{},
+			},
+			want: false,
+		},
+		{
+			name: "collection-not-nil",
+			args: args{
+				it: &Collection{},
+			},
+			want: false,
+		},
+		{
+			name: "activity-not-nil",
+			args: args{
+				it: &Activity{},
+			},
+			want: false,
+		},
+		{
+			name: "intransitive-activity-not-nil",
+			args: args{
+				it: &IntransitiveActivity{},
+			},
+			want: false,
+		},
+		{
+			name: "actor-not-nil",
+			args: args{
+				it: &Actor{},
+			},
+			want: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsNil(tt.args.it); got != tt.want {
+				t.Errorf("IsNil() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

object_test.go

@@ -427,7 +427,7 @@ func TestToObject(t *testing.T) {
 	if err != nil {
 		t.Errorf("Error returned when calling ToObject with activity should be nil, received %s", err)
 	}
-	if a == nil {
+	if IsNil(a) {
 		t.Errorf("Invalid return by ToObject #%v, should have not been nil", a)
 	}
 }

ordered_collection.go

@@ -409,7 +409,7 @@ func (o OrderedCollection) ItemsMatch(col ...Item) bool {
 
 // Equals
 func (o OrderedCollection) Equals(with Item) bool {
-	if with == nil {
+	if IsNil(with) {
 		return false
 	}
 	if !with.IsCollection() {

ordered_collection_page.go

@@ -263,7 +263,7 @@ func (o OrderedCollectionPage) ItemsMatch(col ...Item) bool {
 
 // Equals
 func (o OrderedCollectionPage) Equals(with Item) bool {
-	if with == nil {
+	if IsNil(with) {
 		return false
 	}
 	if !with.IsCollection() {

tests/server_to_server_test.go

@@ -25,7 +25,7 @@ S2S Server: Activities requiring the object property
 	obj := pub.MentionNew("gigel")
 
 	add := pub.AddNew("https://localhost/myactivity", obj, nil)
-	if add.Object == nil {
+	if pub.IsNil(add.Object) {
 		t.Errorf("Missing GetID in Add activity %#v", add.Object)
 	}
 	if add.Object != obj {
@@ -33,7 +33,7 @@ S2S Server: Activities requiring the object property
 	}
 
 	block := pub.BlockNew("https://localhost/myactivity", obj)
-	if block.Object == nil {
+	if pub.IsNil(block.Object) {
 		t.Errorf("Missing GetID in Add activity %#v", block.Object)
 	}
 	if block.Object != obj {
@@ -49,7 +49,7 @@ S2S Server: Activities requiring the object property
 	}
 
 	delete := pub.DeleteNew("https://localhost/myactivity", obj)
-	if delete.Object == nil {
+	if pub.IsNil(delete.Object) {
 		t.Errorf("Missing GetID in Delete activity %#v", delete.Object)
 	}
 	if delete.Object != obj {
@@ -57,7 +57,7 @@ S2S Server: Activities requiring the object property
 	}
 
 	follow := pub.FollowNew("https://localhost/myactivity", obj)
-	if follow.Object == nil {
+	if pub.IsNil(follow.Object) {
 		t.Errorf("Missing GetID in Follow activity %#v", follow.Object)
 	}
 	if follow.Object != obj {
@@ -65,7 +65,7 @@ S2S Server: Activities requiring the object property
 	}
 
 	like := pub.LikeNew("https://localhost/myactivity", obj)
-	if like.Object == nil {
+	if pub.IsNil(like.Object) {
 		t.Errorf("Missing GetID in Like activity %#v", like.Object)
 	}
 	if like.Object != obj {
@@ -73,7 +73,7 @@ S2S Server: Activities requiring the object property
 	}
 
 	update := pub.UpdateNew("https://localhost/myactivity", obj)
-	if update.Object == nil {
+	if pub.IsNil(update.Object) {
 		t.Errorf("Missing GetID in Update activity %#v", update.Object)
 	}
 	if update.Object != obj {
@@ -107,7 +107,7 @@ property: Add, Remove.
 	target := pub.MentionNew("bar")
 
 	add := pub.AddNew("https://localhost/myactivity", obj, target)
-	if add.Target == nil {
+	if pub.IsNil(add.Target) {
 		t.Errorf("Missing Target in Add activity %#v", add.Target)
 	}
 	if add.Target != target {
@@ -115,7 +115,7 @@ property: Add, Remove.
 	}
 
 	remove := pub.RemoveNew("https://localhost/myactivity", obj, target)
-	if remove.Target == nil {
+	if pub.IsNil(remove.Target) {
 		t.Errorf("Missing Target in Remove activity %#v", remove.Target)
 	}
 	if remove.Target != target {