Don't return typed nil interface values

device.go

@@ -62,6 +62,9 @@ func (d *device) IPAddresses() []string {
 
 // Zone implements Device.
 func (d *device) Zone() Zone {
+	if d.zone == nil {
+		return nil
+	}
 	return d.zone
 }
 

device_test.go

@@ -19,6 +19,11 @@ type deviceSuite struct {
 
 var _ = gc.Suite(&deviceSuite{})
 
+func (*deviceSuite) TestNilZone(c *gc.C) {
+	var empty device
+	c.Check(empty.Zone() == nil, jc.IsTrue)
+}
+
 func (*deviceSuite) TestReadDevicesBadSchema(c *gc.C) {
 	_, err := readDevices(twoDotOh, "wat?")
 	c.Check(err, jc.Satisfies, IsDeserializationError)

interface.go

@@ -86,6 +86,9 @@ func (i *interface_) Tags() []string {
 
 // VLAN implements Interface.
 func (i *interface_) VLAN() VLAN {
+	if i.vlan == nil {
+		return nil
+	}
 	return i.vlan
 }
 

interface_test.go

@@ -19,6 +19,11 @@ type interfaceSuite struct {
 
 var _ = gc.Suite(&interfaceSuite{})
 
+func (*interfaceSuite) TestNilVLAN(c *gc.C) {
+	var empty interface_
+	c.Check(empty.VLAN() == nil, jc.IsTrue)
+}
+
 func (*interfaceSuite) TestReadInterfacesBadSchema(c *gc.C) {
 	_, err := readInterfaces(twoDotOh, "wat?")
 	c.Check(err, jc.Satisfies, IsDeserializationError)

link.go

@@ -31,6 +31,9 @@ func (k *link) Mode() string {
 
 // Subnet implements Link.
 func (k *link) Subnet() Subnet {
+	if k.subnet == nil {
+		return nil
+	}
 	return k.subnet
 }
 

link_test.go

@@ -13,6 +13,11 @@ type linkSuite struct{}
 
 var _ = gc.Suite(&linkSuite{})
 
+func (*linkSuite) TestNilSubnet(c *gc.C) {
+	var empty link
+	c.Check(empty.Subnet() == nil, jc.IsTrue)
+}
+
 func (*linkSuite) TestReadLinksBadSchema(c *gc.C) {
 	_, err := readLinks(twoDotOh, "wat?")
 	c.Check(err, jc.Satisfies, IsDeserializationError)

machine.go

@@ -101,11 +101,17 @@ func (m *machine) PowerState() string {
 
 // Zone implements Machine.
 func (m *machine) Zone() Zone {
+	if m.zone == nil {
+		return nil
+	}
 	return m.zone
 }
 
 // BootInterface implements Machine.
 func (m *machine) BootInterface() Interface {
+	if m.bootInterface == nil {
+		return nil
+	}
 	m.bootInterface.controller = m.controller
 	return m.bootInterface
 }

machine_test.go

@@ -19,6 +19,14 @@ type machineSuite struct {
 
 var _ = gc.Suite(&machineSuite{})
 
+func (*machineSuite) TestNilGetters(c *gc.C) {
+	var empty machine
+	c.Check(empty.Zone() == nil, jc.IsTrue)
+	c.Check(empty.PhysicalBlockDevice(0) == nil, jc.IsTrue)
+	c.Check(empty.Interface(0) == nil, jc.IsTrue)
+	c.Check(empty.BootInterface() == nil, jc.IsTrue)
+}
+
 func (*machineSuite) TestReadMachinesBadSchema(c *gc.C) {
 	_, err := readMachines(twoDotOh, "wat?")
 	c.Check(err, jc.Satisfies, IsDeserializationError)

partition.go

@@ -34,6 +34,9 @@ func (p *partition) Path() string {
 
 // FileSystem implements Partition.
 func (p *partition) FileSystem() FileSystem {
+	if p.filesystem == nil {
+		return nil
+	}
 	return p.filesystem
 }
 

partition_test.go

@@ -13,6 +13,11 @@ type partitionSuite struct{}
 
 var _ = gc.Suite(&partitionSuite{})
 
+func (*partitionSuite) TestNilFileSystem(c *gc.C) {
+	var empty partition
+	c.Assert(empty.FileSystem() == nil, jc.IsTrue)
+}
+
 func (*partitionSuite) TestReadPartitionsBadSchema(c *gc.C) {
 	_, err := readPartitions(twoDotOh, "wat?")
 	c.Check(err, jc.Satisfies, IsDeserializationError)

subnet.go

@@ -43,6 +43,9 @@ func (s *subnet) Space() string {
 
 // VLAN implements Subnet.
 func (s *subnet) VLAN() VLAN {
+	if s.vlan == nil {
+		return nil
+	}
 	return s.vlan
 }
 

subnet_test.go

@@ -13,6 +13,11 @@ type subnetSuite struct{}
 
 var _ = gc.Suite(&subnetSuite{})
 
+func (*subnetSuite) TestNilVLAN(c *gc.C) {
+	var empty subnet
+	c.Check(empty.VLAN() == nil, jc.IsTrue)
+}
+
 func (*subnetSuite) TestReadSubnetsBadSchema(c *gc.C) {
 	_, err := readSubnets(twoDotOh, "wat?")
 	c.Assert(err.Error(), gc.Equals, `subnet base schema check failed: expected list, got string("wat?")`)