# Time difference using ruby
**URL:** https://discuss.elastic.co/t/time-difference-using-ruby/173549
**Category:** Logstash
**Created:** [March 22, 2019, 6:32pm UTC](https://discuss.elastic.co/t/time-difference-using-ruby/173549 "2019-03-22T18:32:47Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@elasticforme](https://discuss.elastic.co/u/elasticforme)
#### Post date: [March 22, 2019, 6:32pm UTC](https://discuss.elastic.co/t/time-difference-using-ruby/173549/1 "2019-03-22T18:32:47Z")
I am trying to get a time difference between two time field using ruby filter but looks like one of the timefiled is empty or nill and that is giving me error
ERROR] ruby - Ruby exception occurred: undefined method `-' for nil:NilClass
I am already converting execution\_end to date format above this code.
I don't think database has this field empty.
if [next\_exec\_start] == "nil" or [next\_exec\_start] == "" or [execution\_end] == "" or [execution\_end] == "nil" {
mutate { update =\> { "next\_exec\_start" =\> 0 } }
mutate { add\_field =\> { "next\_exec\_min" =\> 0 } }
}
else {
date { match =\> ["next\_exec\_start", "dd-MMM-yy HH:mm"]
target =\> "next\_exec\_start" }
ruby {
init =\> "require 'time'"
code =\> "event.set('next\_exec\_min',(event.get('next\_exec\_start')-event.get('execution\_end'))/60.round(2))"
}
}
What am I doing wrong. I want to skip ruby operation if next\_exec\_start is not present. but I need that record.
---
### Author:  [@elasticforme](https://discuss.elastic.co/u/elasticforme)
#### Post date: [March 22, 2019, 6:38pm UTC](https://discuss.elastic.co/t/time-difference-using-ruby/173549/2 "2019-03-22T18:38:48Z")
more update, here is the record where I get \_rubyexception
```
{
tags" => [
[0] "_rubyexception"
],
"execution_end" => 2019-03-21T16:31:00.000Z,
"execution_start" => 2019-03-21T14:33:00.000Z,
"next_exec_start" => nil,
}
```
Looks like it is failing when next\_exec\_start is nil but I am trying to replace that with 0 in if statement. looks like I am not comparing something nil might be something else in logstash
---
### Author:  [@elasticforme](https://discuss.elastic.co/u/elasticforme)
#### Post date: [March 22, 2019, 7:10pm UTC](https://discuss.elastic.co/t/time-difference-using-ruby/173549/3 "2019-03-22T19:10:53Z")
ok fixed it myself
nil value is consider nothing in logstash I think
used following and it worked
if ![next\_exec\_start] { assign 0 }
else { do something }
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [April 19, 2019, 7:11pm UTC](https://discuss.elastic.co/t/time-difference-using-ruby/173549/4 "2019-04-19T19:11:03Z")
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