Fixed wrong Mimetype result for null fileName and deleted wrongly pasted javadocs

[Quanzzzz]

Fixed wrong Mimetype result for null fileName to keep consistency with our API contract;
Deleted wrongly pasted javadocs;

Motivation and Context

#1811

Testing

There is no newly added unit test for this change because it's impossible to set the fileName as null here in the path.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

License

• I confirm that this pull request can be released under the Apache 2 license

[codecov-commenter]

Codecov Report

Merging #1901 into master will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1901      +/-   ##
============================================
+ Coverage     76.22%   76.26%   +0.04%     
  Complexity      187      187              
============================================
  Files          1076     1076              
  Lines         32504    32573      +69     
  Branches       2546     2569      +23     
============================================
+ Hits          24775    24841      +66     
- Misses         6468     6474       +6     
+ Partials       1261     1258       -3     

Flag	Coverage Δ	Complexity Δ
#unittests	76.26% <100.00%> (+0.04%)	187.00 <0.00> (ø)

Impacted Files	Coverage Δ	Complexity Δ
...are/amazon/awssdk/core/internal/util/Mimetype.java	85.36% <100.00%> (+4.87%)	0.00 <0.00> (ø)
...tomization/CodegenCustomizationProcessorChain.java	81.81% <0.00%> (-8.19%)	0.00% <0.00%> (ø%)
...on/awssdk/protocols/ion/AwsIonProtocolFactory.java	72.72% <0.00%> (-5.06%)	0.00% <0.00%> (ø%)
.../software/amazon/awssdk/core/sync/RequestBody.java	90.00% <0.00%> (-3.11%)	0.00% <0.00%> (ø%)
...ftware/amazon/awssdk/codegen/internal/Jackson.java	59.09% <0.00%> (-2.82%)	0.00% <0.00%> (ø%)
...on/awssdk/codegen/internal/DocumentationUtils.java	75.00% <0.00%> (-2.42%)	0.00% <0.00%> (ø%)
...nhanced/dynamodb/extensions/WriteModification.java	52.00% <0.00%> (-2.17%)	0.00% <0.00%> (ø%)
...ices/s3/internal/presigner/DefaultS3Presigner.java	88.88% <0.00%> (-1.92%)	0.00% <0.00%> (ø%)
...rvices/s3/internal/ConfiguredS3SdkHttpRequest.java	46.15% <0.00%> (-1.85%)	0.00% <0.00%> (ø%)
...retry/DefaultTokenBucketExceptionCostFunction.java	50.00% <0.00%> (-1.73%)	0.00% <0.00%> (ø%)
... and 42 more

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

100.0% Coverage
0.0% Duplication

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