hapi-fhir ResourceVersionConflictException for Update resource

Question

I am using hapi-fhir sdk in Android. I got ResourceVersionConflictException for Patient update. From api doc

Represents an HTTP 409 Conflict response. This exception should be thrown in methods which accept a version (e.g. Update, Delete) when the operation fails because of a version conflict as specified in the FHIR specification.

how is version conflict happening here. I am just updating Given name and calling client.update()

Here is my sample code;

Patient read:

val patient = client.read()
    .resource(Patient::class.java)
    .withId(id)
    .encodedJson()
    .execute()

Update:

  val newName = .....
  val humanName = if (patient.name == null){
       patient.addName()
  }else{
       if (patient.name.isEmpty()){ patient.addName() } else patient.name[0]
  }
   // updating given name
  if (humanName.given.isEmpty()){
        humanName.addGiven(newName)
  }else{
       humanName.given[0].value = newName
  }

// update api call 
client.update()
    .resource(patient)
    .encodedJson()
    .execute()

I am getting ResourceVersionConflictException for this update call. I am missing something. How can i update patient?

Thanks in advance.