Why check the @nonnull annotation at run time- Why @Nonnull annotation checked at runtime?

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problem ：

I have a function with following signature I have a function with the following signature

public static String myFunction(@Nonnull String param)

When I call it with param as null, I get the following exception: When I use param Call it as null when , I got the following exception ：

Caused by: java.lang.IllegalArgumentException: Argument for @Nonnull parameter 'param' of com/MyClass.myFunction must not be null    at com.MyClass.$$$reportNull$$$0(MyClass.java) 

javax.annotation.Nonnull supposed not to be checked at runtime. You should not check at run time javax.annotation.Nonnull.

Who actually throws the exception and why? Who really throws an exception , Why? ？

PS I run Tomcat server in debug mode from IntelliJ IDEA 2016.3 with Oracle JDK 1.8.0_102PS I use Oracle JDK 1.8.0_102 from IntelliJ IDEA 2016.3 Run in debug mode Tomcat The server

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Solution ：

Reference resources ： https://stackoom.com/en/question/2lOIC