[hudi-1639][hudi-flink] fix BucketAssigner npe

[hk-lrzy]

Tips

• Thank you very much for contributing to Apache Hudi.
• Please review https://hudi.apache.org/contributing.html before opening a pull request.

What is the purpose of the pull request

1. from [HUDI-1624] The state based index should bootstrap from existing base… #2581 (comment)
   fix npe problem when BucketAssignFunction restore from the checkpoint.

2. flink keystate could be access after keycontext'current key be setted，so i move checkPartitionsLoaded into processElement to avoid checkKeyNamespacePreconditions throw exception.

	private void checkKeyNamespacePreconditions(K key, N namespace) {
		Preconditions.checkNotNull(key, "No key set. This method should not be called outside of a keyed context.");
		Preconditions.checkNotNull(namespace, "Provided namespace is null.");
	}

Brief change log

(for example:)

• Modify AnnotationLocation checkstyle rule in checkstyle.xml

Verify this pull request

(Please pick either of the following options)

This pull request is a trivial rework / code cleanup without any test coverage.

(or)

This pull request is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end.
• Added HoodieClientWriteTest to verify the change.
• Manually verified the change by running a job locally.

Committer checklist

• Has a corresponding JIRA in PR title & commit

• Commit message is descriptive of the change

• CI is green

• Necessary doc changes done or have another open PR

• For large changes, please consider breaking it into sub-tasks under an umbrella JIRA.

[lamberken]

@hk-lrzy thanks for yor patch, some conflicts need to be resolved.

[codecov-io]

Codecov Report

Merging #2604 (fed6575) into master (06dc7c7) will decrease coverage by 41.52%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master   #2604       +/-   ##
============================================
- Coverage     51.22%   9.69%   -41.53%     
+ Complexity     3230      48     -3182     
============================================
  Files           438      53      -385     
  Lines         20093    1929    -18164     
  Branches       2069     230     -1839     
============================================
- Hits          10292     187    -10105     
+ Misses         8954    1729     -7225     
+ Partials        847      13      -834     

Flag	Coverage Δ	Complexity Δ
hudicli	?	?
hudiclient	?	?
hudicommon	?	?
hudiflink	?	?
hudihadoopmr	?	?
hudisparkdatasource	?	?
hudisync	?	?
huditimelineservice	?	?
hudiutilities	9.69% <ø> (-59.83%)	0.00 <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
...va/org/apache/hudi/utilities/IdentitySplitter.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-2.00%)
...va/org/apache/hudi/utilities/schema/SchemaSet.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-3.00%)
...a/org/apache/hudi/utilities/sources/RowSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-4.00%)
.../org/apache/hudi/utilities/sources/AvroSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-1.00%)
.../org/apache/hudi/utilities/sources/JsonSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-1.00%)
...rg/apache/hudi/utilities/sources/CsvDFSSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-10.00%)
...g/apache/hudi/utilities/sources/JsonDFSSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-4.00%)
...apache/hudi/utilities/sources/JsonKafkaSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-6.00%)
...pache/hudi/utilities/sources/ParquetDFSSource.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-5.00%)
...lities/schema/SchemaProviderWithPostProcessor.java	0.00% <0.00%> (-100.00%)	0.00% <0.00%> (-4.00%)
... and 414 more