How to generate query based off from user input

Users Dgraph
3

Here is a working example:

Mutation:

{
set {
 _:e1 <ehid> "1" .
 _:c1 <customer_id> "2" .
 _:c1 <subscribes_as> _:e1 .
     
 _:o1 <xcode> "x3" .
 _:o1 <authenticate_as> _:c1 .
}
}

Query (with filter)

{  
 var(func:eq(customer_id, "2")) {
  C_ID AS customer_id
 }

search_by_ehid_using_cust_id_link (func:eq(ehid, "1")) @normalize {
  ~subscribes_as @filter(uid(C_ID))  {
    ~authenticate_as{
      result: xcode
    }
   }
 }     
}

If I pass in customer_id value other than 2, the filter correctly kicks in and no xcode is returned. If however, I dont have a customer_id value at all (and as per your question, this will be an int, so prob be zero in that case ) - i dont want the filter logic to be applied.