@Override
    public boolean equals(Object o) {

        if (this == o) {
            return true;
        }
        if (!(o instanceof IsNull)) {
            return false;
        }

        IsNull isNull = (IsNull) o;

        if (isInnerStream != isNull.isInnerStream) {
            return false;
        }
        if (isFaultStream != isNull.isFaultStream) {
            return false;
        }
        if (streamId != null ? !streamId.equals(isNull.streamId) : isNull.streamId != null) {
            return false;
        }
        if (streamIndex != null ? !streamIndex.equals(isNull.streamIndex) : isNull.streamIndex != null) {
            return false;
        }
        return expression != null ? expression.equals(isNull.expression) : isNull.expression == null;
    }
Condition {@link Expression} checking whether the event is null
modules/siddhi-query-api/src/main/java/io/siddhi/query/api/expression/condition/IsNull.java