public final FunctionCondition notExists() {
        return attribute_not_exists(this);
    }
Returns a <a href=
"http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.SpecifyingConditions.html#ConditionExpressionReference.Functions"
>function condition</a> (that evaluates to true if the attribute referred
to by this path operand does not exist) for building condition
expression.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/xspec/PathOperand.java