public String execute(ComplexEvent event) {
        try {
            return expressionExecutor.execute(event).toString();
        } catch (NullPointerException ex) {
            return null;
        }
    }
Value partition executor computes the partition key based on value of given {@link ComplexEvent} attribute/s.
modules/siddhi-core/src/main/java/io/siddhi/core/partition/executor/ValuePartitionExecutor.java