[GOBBLIN-1714] Prevent silent failure of data copy if files don't exist in source

[AndyJiang99]

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• [ ] My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-1714

Description

• [ ] Here are some details about my PR, including screenshots (if applicable):
• [ ]
• [ ] Throws exception if no files found in source for data copy
• [ ] Doesn't throw exception if no files found in target for data copy as the files will be created

Tests

• [ ] My PR adds the following unit tests OR does not need testing for this extremely good reason:
• [ ] All current tests pass

Commits

• [ ] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[codecov-commenter]

Codecov Report

Merging #3568 (71161bf) into master (78484e2) will decrease coverage by 0.14%. The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #3568      +/-   ##
============================================
- Coverage     46.93%   46.78%   -0.15%     
+ Complexity    10580    10567      -13     
============================================
  Files          2105     2111       +6     
  Lines         82149    82468     +319     
  Branches       9147     9174      +27     
============================================
+ Hits          38558    38586      +28     
- Misses        40050    40323     +273     
- Partials       3541     3559      +18     

Impacted Files	Coverage Δ
...data/management/copy/RecursiveCopyableDataset.java	86.36% <0.00%> (ø)
...blin/data/management/copy/RecursivePathFinder.java	0.00% <0.00%> (-92.86%)	:arrow_down:
...data/management/copy/extractor/EmptyExtractor.java	0.00% <0.00%> (-83.34%)	:arrow_down:
...a/management/copy/hive/HiveLocationDescriptor.java	36.17% <0.00%> (-14.90%)	:arrow_down:
...anagement/copy/hive/UnpartitionedTableFileSet.java	66.66% <0.00%> (-12.97%)	:arrow_down:
...ata/management/copy/hive/HiveCopyEntityHelper.java	51.41% <0.00%> (-11.59%)	:arrow_down:
...ache/gobblin/util/commit/DeleteFileCommitStep.java	34.04% <0.00%> (-8.52%)	:arrow_down:
...a/management/copy/publisher/CopyDataPublisher.java	67.54% <0.00%> (-7.95%)	:arrow_down:
.../hive/filter/LookbackPartitionFilterGenerator.java	78.94% <0.00%> (-5.27%)	:arrow_down:
...ervice/modules/core/GobblinServiceGuiceModule.java	84.74% <0.00%> (-5.26%)	:arrow_down:
... and 24 more

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