Update Asset Object using ScriptRunner in an Automation Rule using Json

[Crystal Rouse]

We are trying to update an asset object in an automation rule by using "

Update Asset with ScriptRuner

The Json works if there is data being passed, but fails for nulls.  We tried the following:

---

{
"objectKey": {{issue.Key.Key.asJsonString}},
"if": {issue.customfield_1.asJsonString.length!=0}
{
"then": {"Description": {{issue.customfield_1.asJsonString}}}
},
"if": {issue.customfield_2.asJsonString.length!=0}
{
"then": {"FieldName": {{issue.customfield_2.asJsonString}}}
}
}

---

I know that we need to check for nulls, but can't get the syntax right.  

If there is any help or documentation, it would be greatly appreciated!