fix: npe in createFrom

[frankyn]

createFrom expects object metadata to be available once uploaded. If response metadata is not available a get object metadata request is made with a null Options parameter which causes an NPE. I tested the change by running IT with multiple uploads to validate failure no longer occurs.

• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)

Fixes #745 ☕️

[codecov]

Codecov Report

Merging #746 (f2950d5) into master (25ea236) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #746      +/-   ##
============================================
+ Coverage     64.60%   64.61%   +0.01%     
  Complexity      625      625              
============================================
  Files            32       32              
  Lines          5311     5313       +2     
  Branches        520      520              
============================================
+ Hits           3431     3433       +2     
  Misses         1718     1718              
  Partials        162      162              

Impacted Files	Coverage Δ	Complexity Δ
...ava/com/google/cloud/storage/BlobWriteChannel.java	80.19% <100.00%> (+0.40%)	15.00 <1.00> (ø)

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