[#2523]fix problem when client api do not provide file parameter

[liubao68]

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[codecov-commenter]

Codecov Report

Merging #4022 (24a23b2) into 2.8.x (09c0886) will decrease coverage by 0.01%.
The diff coverage is 93.75%.

❗ Current head 24a23b2 differs from pull request most recent head 4743046. Consider uploading reports for the commit 4743046 to get more accurate results

@@             Coverage Diff              @@
##              2.8.x    #4022      +/-   ##
============================================
- Coverage     74.20%   74.20%   -0.01%     
- Complexity      703      707       +4     
============================================
  Files          1597     1598       +1     
  Lines         40195    40220      +25     
  Branches       3671     3672       +1     
============================================
+ Hits          29828    29846      +18     
- Misses         8878     8883       +5     
- Partials       1489     1491       +2     

Files	Coverage Δ
...common/rest/codec/param/RestClientRequestImpl.java	87.76% <100.00%> (-0.09%)	⬇️
...oot/springmvc/client/UploadDownloadSchemaTest.java	100.00% <100.00%> (ø)
...t/rest/client/RestClientRequestParametersImpl.java	0.00% <0.00%> (ø)

... and 4 files with indirect coverage changes

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