Fix nil dereference bug in entry checkAuthors

entry.go

@@ -36,6 +36,9 @@ type Entry struct {
 // atom:author element itself.
 func (e *Entry) checkAuthors() error {
 	if e.Authors == nil {
+		if e.Source == nil {
+			return errors.New("no authors set in entry")
+		}
 		if e.Source.Authors == nil {
 			return errors.New("no authors set in entry")
 		}
@@ -64,6 +67,54 @@ func NewEntry(title string) (*Entry, error) {
 	}, nil
 }
 
+// AddAuthor adds the Person as an author to the Entry.
+func (e *Entry) AddAuthor(p *Person) {
+	if e.Authors == nil {
+		e.Authors = make([]*Person, 1)
+		e.Authors[0] = p
+	} else {
+		e.Authors = append(e.Authors, p)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddCategory adds the Category to the Entry.
+func (e *Entry) AddCategory(c *Category) {
+	if e.Categories == nil {
+		e.Categories = make([]*Category, 1)
+		e.Categories[0] = c
+	} else {
+		e.Categories = append(e.Categories, c)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddContributor adds the Person as a contributor to the Entry.
+func (e *Entry) AddContributor(c *Person) {
+	if e.Contributors == nil {
+		e.Contributors = make([]*Person, 1)
+		e.Contributors[0] = c
+	} else {
+		e.Contributors = append(e.Contributors, c)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddLink adds the Link to the Entry.
+func (e *Entry) AddLink(l *Link) {
+	if e.Links == nil {
+		e.Links = make([]*Link, 1)
+		e.Links[0] = l
+	} else {
+		e.Links = append(e.Links, l)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
 // AddExtension adds the ExtensionElement to the Entry.
 func (e *Entry) AddExtension(x *ExtensionElement) {
 	if e.Extensions == nil {