[BUG] Grok NPE fix when JacksonEvent.get() returns null

[graytaylor0]

Description

Grok Prepper was throwing a NPE when a key that did not exist in the event was attempted to match against. If possible, we should try to not have the JacksonEvent get() method return null when no node is found. We should try to return base values of the primitives at the very least, or use an Optional.

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[codecov-commenter]

Codecov Report

Merging #589 (8dd322e) into main (42c5954) will increase coverage by 0.17%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #589      +/-   ##
============================================
+ Coverage     92.12%   92.29%   +0.17%     
  Complexity      569      569              
============================================
  Files            71       71              
  Lines          1727     1727              
  Branches        144      144              
============================================
+ Hits           1591     1594       +3     
+ Misses          105      102       -3     
  Partials         31       31              

Impacted Files	Coverage Δ
...java/com/amazon/dataprepper/pipeline/Pipeline.java	92.85% <0.00%> (+4.28%)	⬆️

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[dlvenable]

I am for returning an Optional on the get. Thanks for making this fix.