Fix create-env bug where an empty slice of disks from the state file results in null being passed to the CPI ask the disks argument

cmd/create_env_test.go

@@ -1,6 +1,7 @@
 package cmd_test
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"path/filepath"
@@ -1144,6 +1145,22 @@ var _ = Describe("CreateEnvCmd", func() {
 				err = command.Run(fakeStage, defaultCreateEnvOpts)
 				Expect(err).NotTo(HaveOccurred())
 			})
+
+			It("constructs and empty array of disks using make, due to odd behavior in golang where empty var []string marshals as null", func() {
+				err := fs.WriteFileString(deploymentStatePath, `
+				{
+					"disks": null
+				}`)
+				Expect(err).ToNot(HaveOccurred())
+
+				expectDeploy.Do(func(_, _, _, _, _, _ interface{}, diskCIDs []string, _ interface{}) {
+					jsonMarshalOfDisks, err := json.Marshal(diskCIDs)
+					Expect(err).ToNot(HaveOccurred())
+					Expect(string(jsonMarshalOfDisks)).To(Equal("[]"))
+				})
+				err = command.Run(fakeStage, defaultCreateEnvOpts)
+				Expect(err).NotTo(HaveOccurred())
+			})
 		})
 	})
 })

cmd/deployment_preparer.go

@@ -307,7 +307,7 @@ func (c *DeploymentPreparer) stemcellApiVersion(stemcell bistemcell.ExtractedSte
 
 // These disk CIDs get passed all the way to the create_vm cpi call
 func (c *DeploymentPreparer) extractDiskCIDsFromState(deploymentState biconfig.DeploymentState) []string {
-	var diskCIDs []string
+	diskCIDs := make([]string, 0)
 	for _, disk := range deploymentState.Disks {
 		diskCIDs = append(diskCIDs, disk.CID)
 	}