{
  "version": "2017-02-28",
  "operation": "UpdateItem",
  "key": {
    "id": $util.dynamodb.toDynamoDBJson($ctx.args.input.id),
  },

  ## Set up some space to keep track of things we're updating **
  #set( $expNames  = {} )
  #set( $expValues = {} )
  #set( $expSet = {} )
  #set( $expAdd = {} )
  #set( $expRemove = [] )

  ## Iterate through each argument, skipping keys **
  #foreach( $entry in $util.map.copyAndRemoveAllKeys($ctx.args.input, ["id"]).entrySet() )
    #if( $util.isNull($entry.value) )
      ## If the argument is set to "null", then remove that attribute from the item in DynamoDB **

      #set( $discard = ${expRemove.add("#${entry.key}")} )
      $!{expNames.put("#${entry.key}", "${entry.key}")}
    #else
      ## Otherwise set (or update) the attribute on the item in DynamoDB **

      $!{expSet.put("#${entry.key}", ":${entry.key}")}
      $!{expNames.put("#${entry.key}", "${entry.key}")}
      $!{expValues.put(":${entry.key}", $util.dynamodb.toDynamoDB($entry.value))}
    #end
  #end

  ## Start building the update expression, starting with attributes we're going to SET **
  #set( $expression = "" )
  #if( !${expSet.isEmpty()} )
    #set( $expression = "SET" )
    #foreach( $entry in $expSet.entrySet() )
      #set( $expression = "${expression} ${entry.key} = ${entry.value}" )
      #if ( $foreach.hasNext )
        #set( $expression = "${expression}," )
      #end
    #end
  #end

  ## Continue building the update expression, adding attributes we're going to ADD **
  #if( !${expAdd.isEmpty()} )
    #set( $expression = "${expression} ADD" )
    #foreach( $entry in $expAdd.entrySet() )
      #set( $expression = "${expression} ${entry.key} ${entry.value}" )
      #if ( $foreach.hasNext )
        #set( $expression = "${expression}," )
      #end
    #end
  #end

  ## Continue building the update expression, adding attributes we're going to REMOVE **
  #if( !${expRemove.isEmpty()} )
    #set( $expression = "${expression} REMOVE" )

    #foreach( $entry in $expRemove )
      #set( $expression = "${expression} ${entry}" )
      #if ( $foreach.hasNext )
        #set( $expression = "${expression}," )
      #end
    #end
  #end

  ## Finally, write the update expression into the document, along with any expressionNames and expressionValues **
  "update": {
    "expression": "${expression}",
    #if( !${expNames.isEmpty()} )
      "expressionNames": $utils.toJson($expNames),
    #end
    #if( !${expValues.isEmpty()} )
      "expressionValues": $utils.toJson($expValues),
    #end
  },

  "condition": {
    "expression": "attribute_exists(#id)",
    "expressionNames": {
      "#id": "id",
    },
  }
}