Add safety net when running sections with null inputs

[sovdeeth]

Is your feature request related to a problem? Please describe.
When running a section, say, with 2 inputs and you provide a null input as the first one, an AIIOB will be thrown when it tries to set the (second?) variable.

Describe the solution you'd like
No exception should be thrown, the variable should stay unset.

Describe alternatives you've considered
This should be a simple check in Section#run()

Additional context
Provided stacktrace from user:

[19:42:44 WARN]: [skript-reflect] Plugin skript-reflect v2.4 generated an exception while executing task 32
java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
        at ch.njol.skript.lang.Variable.change(Variable.java:550) ~[Skript.jar:?]
        at com.btk5h.skriptmirror.skript.reflect.sections.Section.run(Section.java:35) ~[skript-reflect.jar:?]
        at com.btk5h.skriptmirror.skript.reflect.sections.EffRunSection.lambda$walk$2(EffRunSection.java:95) ~[skript-reflect.jar:?]
        at org.bukkit.craftbukkit.v1_20_R3.scheduler.CraftTask.run(CraftTask.java:101) ~[purpur-1.20.4.jar:git-Purpur-2118]
        at org.bukkit.craftbukkit.v1_20_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:57) ~[purpur-1.20.4.jar:git-Purpur-2118]
        at com.destroystokyo.paper.ServerSchedulerReportingWrapper.run(ServerSchedulerReportingWrapper.java:22) ~[purpur-1.20.4.jar:?]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) ~[?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) ~[?:?]
        at java.lang.Thread.run(Thread.java:840) ~[?:?]

when running

run section {ask_command_handler} async with player's uuid, arg-1

in a command as console, leading player's uuid to be unset.

[Vulcano771]

Should be fixed by my pr #102