implement json.Unmarshaler for Server
diff --git a/openstack/compute/v2/servers/results.go b/openstack/compute/v2/servers/results.go
index 4237481..7659c75 100644
--- a/openstack/compute/v2/servers/results.go
+++ b/openstack/compute/v2/servers/results.go
@@ -3,6 +3,7 @@
 import (
 	"crypto/rsa"
 	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"net/url"
 	"path"
@@ -129,58 +130,68 @@
 type Server struct {
 	// ID uniquely identifies this server amongst all other servers, including those not accessible to the current tenant.
 	ID string `json:"id"`
-
 	// TenantID identifies the tenant owning this server resource.
 	TenantID string `json:"tenant_id"`
-
 	// UserID uniquely identifies the user account owning the tenant.
 	UserID string `json:"user_id"`
-
 	// Name contains the human-readable name for the server.
 	Name string `json:"name"`
-
 	// Updated and Created contain ISO-8601 timestamps of when the state of the server last changed, and when it was created.
 	Updated string
 	Created string
-
-	HostID string
-
+	HostID  string
 	// Status contains the current operational status of the server, such as IN_PROGRESS or ACTIVE.
 	Status string
-
 	// Progress ranges from 0..100.
 	// A request made against the server completes only once Progress reaches 100.
 	Progress int
-
 	// AccessIPv4 and AccessIPv6 contain the IP addresses of the server, suitable for remote access for administration.
 	AccessIPv4, AccessIPv6 string
-
 	// Image refers to a JSON object, which itself indicates the OS image used to deploy the server.
 	Image map[string]interface{}
-
 	// Flavor refers to a JSON object, which itself indicates the hardware configuration of the deployed server.
 	Flavor map[string]interface{}
-
 	// Addresses includes a list of all IP addresses assigned to the server, keyed by pool.
 	Addresses map[string]interface{}
-
 	// Metadata includes a list of all user-specified key-value pairs attached to the server.
 	Metadata map[string]interface{}
-
 	// Links includes HTTP references to the itself, useful for passing along to other APIs that might want a server reference.
 	Links []interface{}
-
 	// KeyName indicates which public key was injected into the server on launch.
 	KeyName string `json:"key_name"`
-
 	// AdminPass will generally be empty ("").  However, it will contain the administrative password chosen when provisioning a new server without a set AdminPass setting in the first place.
 	// Note that this is the ONLY time this field will be valid.
 	AdminPass string `json:"adminPass"`
-
 	// SecurityGroups includes the security groups that this instance has applied to it
 	SecurityGroups []map[string]interface{} `json:"security_groups"`
 }
 
+func (s *Server) UnmarshalJSON(b []byte) error {
+	type tmp Server
+	var server *struct {
+		tmp
+		Image interface{}
+	}
+	err := json.Unmarshal(b, &server)
+	if err != nil {
+		return err
+	}
+
+	*s = Server(server.tmp)
+
+	switch t := server.Image.(type) {
+	case map[string]interface{}:
+		s.Image = t
+	case string:
+		switch t {
+		case "":
+			s.Image = nil
+		}
+	}
+
+	return nil
+}
+
 // ServerPage abstracts the raw results of making a List() request against the API.
 // As OpenStack extensions may freely alter the response bodies of structures returned to the client, you may only safely access the
 // data provided through the ExtractServers call.
diff --git a/openstack/compute/v2/servers/testing/fixtures.go b/openstack/compute/v2/servers/testing/fixtures.go
index b4fb7ff..613dc1e 100644
--- a/openstack/compute/v2/servers/testing/fixtures.go
+++ b/openstack/compute/v2/servers/testing/fixtures.go
@@ -154,7 +154,69 @@
 			"OS-EXT-STS:power_state": 1,
 			"config_drive": "",
 			"metadata": {}
-		}
+		},
+		{
+		"status": "ACTIVE",
+		"updated": "2014-09-25T13:04:49Z",
+		"hostId": "29d3c8c896a45aa4c34e52247875d7fefc3d94bbcc9f622b5d204362",
+		"OS-EXT-SRV-ATTR:host": "devstack",
+		"addresses": {
+			"private": [
+				{
+					"OS-EXT-IPS-MAC:mac_addr": "fa:16:3e:9e:89:be",
+					"version": 4,
+					"addr": "10.0.0.31",
+					"OS-EXT-IPS:type": "fixed"
+				}
+			]
+		},
+		"links": [
+			{
+				"href": "http://104.130.131.164:8774/v2/fcad67a6189847c4aecfa3c81a05783b/servers/9e5476bd-a4ec-4653-93d6-72c93aa682ba",
+				"rel": "self"
+			},
+			{
+				"href": "http://104.130.131.164:8774/fcad67a6189847c4aecfa3c81a05783b/servers/9e5476bd-a4ec-4653-93d6-72c93aa682ba",
+				"rel": "bookmark"
+			}
+		],
+		"key_name": null,
+		"image": "",
+		"OS-EXT-STS:task_state": null,
+		"OS-EXT-STS:vm_state": "active",
+		"OS-EXT-SRV-ATTR:instance_name": "instance-0000001d",
+		"OS-SRV-USG:launched_at": "2014-09-25T13:04:49.000000",
+		"OS-EXT-SRV-ATTR:hypervisor_hostname": "devstack",
+		"flavor": {
+			"id": "1",
+			"links": [
+				{
+					"href": "http://104.130.131.164:8774/fcad67a6189847c4aecfa3c81a05783b/flavors/1",
+					"rel": "bookmark"
+				}
+			]
+		},
+		"id": "9e5476bd-a4ec-4653-93d6-72c93aa682bb",
+		"security_groups": [
+			{
+				"name": "default"
+			}
+		],
+		"OS-SRV-USG:terminated_at": null,
+		"OS-EXT-AZ:availability_zone": "nova",
+		"user_id": "9349aff8be7545ac9d2f1d00999a23cd",
+		"name": "merp",
+		"created": "2014-09-25T13:04:41Z",
+		"tenant_id": "fcad67a6189847c4aecfa3c81a05783b",
+		"OS-DCF:diskConfig": "MANUAL",
+		"os-extended-volumes:volumes_attached": [],
+		"accessIPv4": "",
+		"accessIPv6": "",
+		"progress": 0,
+		"OS-EXT-STS:power_state": 1,
+		"config_drive": "",
+		"metadata": {}
+	}
 	]
 }
 `
@@ -353,6 +415,54 @@
 			},
 		},
 	}
+
+	// ServerMerp is a Server struct that should correspond to the second server in ServerListBody.
+	ServerMerp = servers.Server{
+		Status:  "ACTIVE",
+		Updated: "2014-09-25T13:04:49Z",
+		HostID:  "29d3c8c896a45aa4c34e52247875d7fefc3d94bbcc9f622b5d204362",
+		Addresses: map[string]interface{}{
+			"private": []interface{}{
+				map[string]interface{}{
+					"OS-EXT-IPS-MAC:mac_addr": "fa:16:3e:9e:89:be",
+					"version":                 float64(4),
+					"addr":                    "10.0.0.31",
+					"OS-EXT-IPS:type":         "fixed",
+				},
+			},
+		},
+		Links: []interface{}{
+			map[string]interface{}{
+				"href": "http://104.130.131.164:8774/v2/fcad67a6189847c4aecfa3c81a05783b/servers/9e5476bd-a4ec-4653-93d6-72c93aa682ba",
+				"rel":  "self",
+			},
+			map[string]interface{}{
+				"href": "http://104.130.131.164:8774/fcad67a6189847c4aecfa3c81a05783b/servers/9e5476bd-a4ec-4653-93d6-72c93aa682ba",
+				"rel":  "bookmark",
+			},
+		},
+		Image: nil,
+		Flavor: map[string]interface{}{
+			"id": "1",
+			"links": []interface{}{
+				map[string]interface{}{
+					"href": "http://104.130.131.164:8774/fcad67a6189847c4aecfa3c81a05783b/flavors/1",
+					"rel":  "bookmark",
+				},
+			},
+		},
+		ID:       "9e5476bd-a4ec-4653-93d6-72c93aa682bb",
+		UserID:   "9349aff8be7545ac9d2f1d00999a23cd",
+		Name:     "merp",
+		Created:  "2014-09-25T13:04:41Z",
+		TenantID: "fcad67a6189847c4aecfa3c81a05783b",
+		Metadata: map[string]interface{}{},
+		SecurityGroups: []map[string]interface{}{
+			map[string]interface{}{
+				"name": "default",
+			},
+		},
+	}
 )
 
 type CreateOptsWithCustomField struct {
diff --git a/openstack/compute/v2/servers/testing/requests_test.go b/openstack/compute/v2/servers/testing/requests_test.go
index 7db6b93..6d792d5 100644
--- a/openstack/compute/v2/servers/testing/requests_test.go
+++ b/openstack/compute/v2/servers/testing/requests_test.go
@@ -26,11 +26,12 @@
 			return false, err
 		}
 
-		if len(actual) != 2 {
-			t.Fatalf("Expected 2 servers, got %d", len(actual))
+		if len(actual) != 3 {
+			t.Fatalf("Expected 3 servers, got %d", len(actual))
 		}
 		th.CheckDeepEquals(t, ServerHerp, actual[0])
 		th.CheckDeepEquals(t, ServerDerp, actual[1])
+		th.CheckDeepEquals(t, ServerMerp, actual[2])
 
 		return true, nil
 	})