[improve][client]Add null check for Pulsar client clock configuration

[3pacccccc]

Motivation

Currently, when setting a clock for the Pulsar client, there is no null check for the clock parameter. This can cause a NullPointerException when sending messages if a null clock is passed.1

Modifications

This PR adds a null check for the clock parameter to provide a clear error message and prevent NPEs.

Verifying this change

• Make sure that the change passes the CI checks.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: 3pacccccc#26

[3pacccccc]

BTW, For custom clock implementations, if the millis() method returns abnormal data (such as negative numbers(eg. -1), extremely large values(eg. 9999999999)) or throws exceptions directly, these cases are not validated. Such validations should be considered? any suggestions?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.02%. Comparing base (461ffd8) to head (751a34f).
⚠️ Report is 14 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #24848      +/-   ##
============================================
- Coverage     74.36%   74.02%   -0.34%     
+ Complexity    33856    32641    -1215     
============================================
  Files          1913     1913              
  Lines        149280   152228    +2948     
  Branches      17324    18163     +839     
============================================
+ Hits         111012   112690    +1678     
- Misses        29445    30515    +1070     
- Partials       8823     9023     +200     

Flag	Coverage Δ
inttests	27.27% <0.00%> (+0.62%)	⬆️
systests	23.24% <0.00%> (+0.38%)	⬆️
unittests	73.41% <100.00%> (-0.48%)	⬇️

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Files with missing lines	Coverage Δ
...g/apache/pulsar/client/impl/ClientBuilderImpl.java	87.02% <100.00%> (+0.07%)	⬆️

... and 92 files with indirect coverage changes

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