fix: Handle empty custom fields correctly

Empty custom fields should be passed as nil to Netbox and nil values
from Netbox should be passed to Terraform as an empty string.

Netbox distingushes between an Empty string and null so this behaviour
mirrors the web UI.

netbox/util.go

@@ -187,7 +187,6 @@ func convertArrayInterfaceString(arrayInterface []interface{}) string {
 
 // Pick the custom fields in the state file and update values with data from API
 func updateCustomFieldsFromAPI(stateCustomFields, customFields interface{}) []map[string]string {
-
 	var tfCms []map[string]string
 
 	switch t := customFields.(type) {
@@ -196,11 +195,12 @@ func updateCustomFieldsFromAPI(stateCustomFields, customFields interface{}) []ma
 			for key, value := range t {
 				if stateCustomField.(map[string]interface{})["name"].(string) == key {
 					var strValue string
-					if value != nil {
-						cm := map[string]string{}
-						cm["name"] = key
-						cm["type"] = stateCustomField.(map[string]interface{})["type"].(string)
 
+					cm := map[string]string{}
+					cm["name"] = key
+					cm["type"] = stateCustomField.(map[string]interface{})["type"].(string)
+
+					if value != nil {
 						switch v := value.(type) {
 						case []interface{}:
 							strValue = convertArrayInterfaceString(v)
@@ -215,8 +215,11 @@ func updateCustomFieldsFromAPI(stateCustomFields, customFields interface{}) []ma
 						}
 
 						cm["value"] = strValue
-						tfCms = append(tfCms, cm)
+					} else {
+						cm["value"] = ""
 					}
+
+					tfCms = append(tfCms, cm)
 				}
 			}
 		}
@@ -241,23 +244,26 @@ func convertCustomFieldsFromTerraformToAPI(stateCustomFields []interface{}, cust
 		cfType := customField["type"].(string)
 		cfValue := customField["value"].(string)
 
-		if cfType == "integer" {
-			cfValueInt, _ := strconv.Atoi(cfValue)
-			toReturn[cfName] = cfValueInt
-		} else if cfType == CustomFieldBoolean {
-			if cfValue == "true" {
-				toReturn[cfName] = true
-			} else if cfValue == "false" {
-				toReturn[cfName] = false
+		if len(cfValue) > 0 {
+			if cfType == "integer" {
+				cfValueInt, _ := strconv.Atoi(cfValue)
+				toReturn[cfName] = cfValueInt
+			} else if cfType == CustomFieldBoolean {
+				if cfValue == "true" {
+					toReturn[cfName] = true
+				} else if cfValue == "false" {
+					toReturn[cfName] = false
+				}
+			} else if cfType == "multiple" {
+				cfValueArray := strings.Split(cfValue, ",")
+				sort.Strings(cfValueArray)
+				toReturn[cfName] = cfValueArray
+			} else {
+				toReturn[cfName] = cfValue
 			}
-		} else if cfType == "multiple" {
-			cfValueArray := strings.Split(cfValue, ",")
-			sort.Strings(cfValueArray)
-			toReturn[cfName] = cfValueArray
 		} else {
-			toReturn[cfName] = cfValue
+			toReturn[cfName] = nil
 		}
-
 	}
 
 	return toReturn