support nullable params

cli/azd/pkg/azure/arm_template.go

@@ -112,6 +112,7 @@ type ArmTemplateParameterDefinition struct {
 	Ref                  string                                         `json:"$ref"`
 	Properties           ArmTemplateParameterDefinitions                `json:"properties,omitempty"`
 	AdditionalProperties *ArmTemplateParameterAdditionalPropertiesValue `json:"additionalProperties,omitempty"`
+	Nullable             *bool                                          `json:"nullable,omitempty"`
 }
 
 func (d *ArmTemplateParameterDefinition) Secure() bool {

cli/azd/pkg/infra/provisioning/bicep/bicep_provider.go

@@ -1860,6 +1860,11 @@ func (p *BicepProvider) ensureParameters(
 			continue
 		}
 
+		if param.Nullable != nil && *param.Nullable {
+			// If the parameter is nullable, we can skip prompting for it.
+			continue
+		}
+
 		// This required parameter was not in parameters file - see if we stored a value in config from an earlier
 		// prompt and if so use it.
 		configKey := fmt.Sprintf("infra.parameters.%s", key)

cli/azd/test/functional/testdata/samples/storage/infra/main.bicep

@@ -25,6 +25,10 @@ param secureValue string
 @secure()
 param secureObject object = {}
 
+// tests should not prompt for this parameter
+param nullableParam string?
+output nullableParamOutput string? = nullableParam
+
 var tags = {
   'azd-env-name': environmentName
   DeleteAfter: deleteAfterTime