# NullPointer while launching Gatling on Docker

**URL:** <https://community.gatling.io/t/nullpointer-while-launching-gatling-on-docker/4975>\
**Category:** Gatling (Open-Source)\
**Created:** [April 26, 2019, 2:24pm UTC](https://community.gatling.io/t/nullpointer-while-launching-gatling-on-docker/4975 "2019-04-26T14:24:26Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Clarence\_Dimitri\_CHA](https://avatars.discourse-cdn.com/v4/letter/c/67e7ee/32.png) [@Clarence\_Dimitri\_CHA](https://community.gatling.io/u/Clarence_Dimitri_CHA)\
**Post date:** [April 26, 2019, 2:24pm UTC](https://community.gatling.io/t/nullpointer-while-launching-gatling-on-docker/4975/1 "2019-04-26T14:24:26Z")

</div>

I have a weird behavior when launching Gatling in Docker.

I am using docker compose and when I try to use the image denvazh/gatling to launch gatling with the command command: ["-sf", “/gatling-demo/src/test/scala”]

The error that displays is :

gatling\_1 | perfAdvisor.PerfAdvisorSimulation is the only simulation, executing it.

gatling\_1 | Select run description (optional)  
gatling\_1 | 14:05:10.069 [ERROR] i.g.a.Gatling$ - Run crashed  
gatling\_1 | java.lang.NullPointerException: null  
gatling\_1 | at io.gatling.app.Selection$Selector.askRunDescription(Selection.scala:133)  
gatling\_1 | at io.gatling.app.Selection$Selector.$anonfun$selection$5(Selection.scala:59)  
gatling\_1 | at scala.Option.getOrElse(Option.scala:121)  
gatling\_1 | at io.gatling.app.Selection$Selector.selection(Selection.scala:59)  
gatling\_1 | at io.gatling.app.Selection$.apply(Selection.scala:36)  
gatling\_1 | at io.gatling.app.Runner.run0(Runner.scala:74)  
gatling\_1 | at io.gatling.app.Runner.run(Runner.scala:61)  
gatling\_1 | at io.gatling.app.Gatling$.start(Gatling.scala:74)  
gatling\_1 | at io.gatling.app.Gatling$.fromArgs(Gatling.scala:47)  
gatling\_1 | at io.gatling.app.Gatling$.main(Gatling.scala:39)  
gatling\_1 | at io.gatling.app.Gatling.main(Gatling.scala)  
gatling\_1 | Exception in thread “main” java.lang.NullPointerException  
gatling\_1 | at io.gatling.app.Selection$Selector.askRunDescription(Selection.scala:133)  
gatling\_1 | at io.gatling.app.Selection$Selector.$anonfun$selection$5(Selection.scala:59)  
gatling\_1 | at scala.Option.getOrElse(Option.scala:121)  
gatling\_1 | at io.gatling.app.Selection$Selector.selection(Selection.scala:59)  
gatling\_1 | at io.gatling.app.Selection$.apply(Selection.scala:36)  
gatling\_1 | at io.gatling.app.Runner.run0(Runner.scala:74)  
gatling\_1 | at io.gatling.app.Runner.run(Runner.scala:61)  
gatling\_1 | at io.gatling.app.Gatling$.start(Gatling.scala:74)  
gatling\_1 | at io.gatling.app.Gatling$.fromArgs(Gatling.scala:47)  
gatling\_1 | at io.gatling.app.Gatling$.main(Gatling.scala:39)  
gatling\_1 | at io.gatling.app.Gatling.main(Gatling.scala)  
gatling-perfadvisor\_gatling\_1 exited with code 1

However when I launch gatling on my machine with **./gatling.sh -sf ./my-project/src/test/scala** , it displays :

gatling\_1 | perfAdvisor.PerfAdvisorSimulation is the only simulation, executing it.  
gatling\_1 | Select run description (optional)

and I have to press enter to start the simulations.

When I try to launch the simulations by providing the full path of the class name : **./gatling.sh -s /my-project/src/test/scala/my-package/MySimulation.scala** :

java.lang.ClassNotFoundException: src/test/scala/my-package/MySimulation.scala  
at java.base/java.lang.Class.forName0(Native Method)  
at java.base/java.lang.Class.forName(Class.java:315)  
at io.gatling.app.Selection$Selector.$anonfun$singleSimulationFromConfig$2(Selection.scala:70)  
at scala.util.Try$.apply(Try.scala:213)  
at io.gatling.app.Selection$Selector.findUserDefinedSimulationInClassloader$1(Selection.scala:70)  
… 15 common frames omitted  
Wrapped by: java.lang.IllegalArgumentException: User defined Simulation class src/test/scala/my-package/MySimulation.scala could not be loaded  
at io.gatling.app.Selection$Selector.findUserDefinedSimulationInClassloader$1(Selection.scala:79)  
at io.gatling.app.Selection$Selector.$anonfun$singleSimulationFromConfig$4(Selection.scala:84)  
at scala.Option.orElse(Option.scala:306)  
at io.gatling.app.Selection$Selector.$anonfun$singleSimulationFromConfig$3(Selection.scala:84)  
at scala.Option.flatMap(Option.scala:188)  
at io.gatling.app.Selection$Selector.singleSimulationFromConfig(Selection.scala:82)  
at io.gatling.app.Selection$Selector.$anonfun$selection$1(Selection.scala:52)  
at scala.Option.getOrElse(Option.scala:138)  
at io.gatling.app.Selection$Selector.selection(Selection.scala:44)  
at io.gatling.app.Selection$.apply(Selection.scala:36)  
at io.gatling.app.Runner.run0(Runner.scala:73)  
at io.gatling.app.Runner.run(Runner.scala:60)  
at io.gatling.app.Gatling$.start(Gatling.scala:73)  
at io.gatling.app.Gatling$.fromArgs(Gatling.scala:46)  
at io.gatling.app.Gatling$.main(Gatling.scala:38)  
at io.gatling.app.Gatling.main(Gatling.scala)  
Exception in thread “main” java.lang.IllegalArgumentException: User defined Simulation class src/test/scala/my-package/MySimulation.scala could not be loaded  
at io.gatling.app.Selection$Selector.findUserDefinedSimulationInClassloader$1(Selection.scala:79)  
at io.gatling.app.Selection$Selector.$anonfun$singleSimulationFromConfig$4(Selection.scala:84)  
at scala.Option.orElse(Option.scala:306)  
at io.gatling.app.Selection$Selector.$anonfun$singleSimulationFromConfig$3(Selection.scala:84)  
at scala.Option.flatMap(Option.scala:188)  
at io.gatling.app.Selection$Selector.singleSimulationFromConfig(Selection.scala:82)  
at io.gatling.app.Selection$Selector.$anonfun$selection$1(Selection.scala:52)  
at scala.Option.getOrElse(Option.scala:138)  
at io.gatling.app.Selection$Selector.selection(Selection.scala:44)  
at io.gatling.app.Selection$.apply(Selection.scala:36)  
at io.gatling.app.Runner.run0(Runner.scala:73)  
at io.gatling.app.Runner.run(Runner.scala:60)  
at io.gatling.app.Gatling$.start(Gatling.scala:73)  
at io.gatling.app.Gatling$.fromArgs(Gatling.scala:46)  
at io.gatling.app.Gatling$.main(Gatling.scala:38)  
at io.gatling.app.Gatling.main(Gatling.scala)  
Caused by: java.lang.ClassNotFoundException: src/test/scala/my-package/MySimulation.scala  
at java.base/java.lang.Class.forName0(Native Method)  
at java.base/java.lang.Class.forName(Class.java:315)  
at io.gatling.app.Selection$Selector.$anonfun$singleSimulationFromConfig$2(Selection.scala:70)  
at scala.util.Try$.apply(Try.scala:213)  
at io.gatling.app.Selection$Selector.findUserDefinedSimulationInClassloader$1(Selection.scala:70)  
… 15 more

Is there an equivalent of “-y” option like in apt-get so we can launch the simulations automatically.

Thx for your response

Clarence

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<div class="post-metadata">

**Author:** ![notdryft](https://dub1.discourse-cdn.com/flex013/user_avatar/community.gatling.io/notdryft/32/1103_2.png) [@notdryft](https://community.gatling.io/u/notdryft)\
**Post date:** [April 26, 2019, 3:03pm UTC](https://community.gatling.io/t/nullpointer-while-launching-gatling-on-docker/4975/2 "2019-04-26T15:03:39Z")

</div>

Inputing a run description with -rd is what you are looking for: [https://gatling.io/docs/current/general/configuration/](https://gatling.io/docs/current/general/configuration/)