Protect against panic when unprotecting state with no resources

Fixes: #4405

CHANGELOG.md

@@ -6,6 +6,9 @@ CHANGELOG
 - Add support for a `PULUMI_CONSOLE_DOMAIN` environment variable to override the
   behavior for how URLs to the Pulumi Console are generated.
   [#4410](https://github.com/pulumi/pulumi/pull/4410)
+  
+- Protect against panic when unprotecting non-existant resources
+  [#4441](https://github.com/pulumi/pulumi/pull/4441)
 
 ## 2.0.0 (2020-04-16)
 =======

pkg/cmd/pulumi/state_unprotect.go

@@ -68,6 +68,11 @@ This command clears the 'protect' bit on one or more resources, allowing those r
 
 func unprotectAllResources(stackName string, showPrompt bool) result.Result {
 	res := runTotalStateEdit(stackName, showPrompt, func(_ display.Options, snap *deploy.Snapshot) error {
+		// Protects against Panic when a user tries to unprotect non-existing resources
+		if snap == nil {
+			return fmt.Errorf("no resources found to unprotect")
+		}
+
 		for _, res := range snap.Resources {
 			err := edit.UnprotectResource(snap, res)
 			contract.AssertNoError(err)