added test to illustrate wrong behavior

builder/amazon/common/block_device_test.go

@@ -36,6 +36,23 @@ func TestBlockDevice(t *testing.T) {
 				},
 			},
 		},
+		{
+			Config: &BlockDevice{
+				DeviceName:          "/dev/sdb",
+				VolumeSize:          8,
+			},
+
+			Result: &ec2.BlockDeviceMapping{
+				DeviceName:  aws.String("/dev/sdb"),
+				VirtualName: aws.String(""),
+				EBS: &ec2.EBSBlockDevice{
+					Encrypted:           aws.Boolean(false),
+					VolumeType:          aws.String(""),
+					VolumeSize:          aws.Long(8),
+					DeleteOnTermination: aws.Boolean(false),
+				},
+			},
+		},
 		{
 			Config: &BlockDevice{
 				DeviceName:          "/dev/sdb",