AWS: Fix CLASSPATH to prevent NULL entry

[MrSerth]

Since the CLASSPATH is not set already, the previous solution created the following path:

".:/var/task/lib/org.hamcrest.hamcrest-3.0.jar:/var/task/lib/junit.junit-4.13.2.jar:null"

Now, we create the following:

".:/var/task/lib/org.hamcrest.hamcrest-3.0.jar:/var/task/lib/junit.junit-4.13.2.jar"

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.19%. Comparing base (636a30e) to head (4f55a34).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #696      +/-   ##
==========================================
+ Coverage   76.11%   76.19%   +0.08%     
==========================================
  Files          43       43              
  Lines        3676     3676              
==========================================
+ Hits         2798     2801       +3     
+ Misses        642      640       -2     
+ Partials      236      235       -1     

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