Fix issue when we're sending in empty vars to Nomad

This fixes one issue where the Nomad job doesn't accept any variables
which results in a KeyError, and speeds up cases where we are not
passing in variables

pulumi/infra/nomad_job.py

@@ -98,16 +98,18 @@ def _fix_pulumi_preview(
     ) -> NomadVars:
         """
         This is a hack to deal with issues around pulumi preview.
-        The Problem: Specifically, during pulumi preview, pulumi Output objects never resolve into strings or other types. This means that if a PR creates a new resource and then tries to use that resource's attributes in a Nomad variable, there's a type error because Pulumi object != string. Frustratingly, this manifests as a variable unset error for ALL Nomad variables in the file. This can also happen if a project is being pulumi'd up with no existing resources.
+        The Problem: Specifically, during pulumi preview, pulumi Output objects never resolve into strings or other
+        types. This means that if a PR creates a new resource and then tries to use that resource's attributes in a
+        Nomad variable, there's a type error because Pulumi object != string. Frustratingly, this manifests as a
+        variable unset error for ALL Nomad variables in the file. This can also happen if a project is being pulumi'd up
+        with no existing resources.
 
         The Solution:
-        We're using reflection to parse the Nomad file's input variable types. We're then mocking the primitives types (str, bool, number) with fake value
-
-
-
-
+        We're using reflection to parse the Nomad file's input variable types. We're then mocking the primitives types
+        (str, bool, number) with fake values
         """
-        if pulumi.runtime.is_dry_run():
+        # short circuit if there are no variables to parse
+        if pulumi.runtime.is_dry_run() and len(vars) >= 1:
 
             hcl2_parser = HCL2TypeParser().parser
             with open(jobspec) as file: