ParseUserData: return nil on empty input string

initialize/user_data.go

@@ -9,6 +9,9 @@ import (
 )
 
 func ParseUserData(contents string) (interface{}, error) {
+	if len(contents) == 0 {
+		return nil, nil
+	}
 	header := strings.SplitN(contents, "\n", 2)[0]
 
 	// Explicitly trim the header so we can handle user-data from

initialize/user_data_test.go

@@ -47,3 +47,12 @@ func TestParseConfigCRLF(t *testing.T) {
 		t.Error("Parsed incorrect number of SSH keys")
 	}
 }
+
+func TestParseConfigEmpty(t *testing.T) {
+	i, e := ParseUserData(``)
+	if i != nil {
+		t.Error("ParseUserData of empty string returned non-nil unexpectedly")
+	} else if e != nil {
+		t.Error("ParseUserData of empty string returned error unexpectedly")
+	}
+}