fix: storing an empty Buffer

[vicb]

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As discussed in #755 datastore can not currently store an empty buffer due to a bug in protobufjs - see protobufjs/protobuf.js#1500.

However protobufs supports 2 way of passing a buffer, as seen in converter.js:

            case "bytes": gen
                ("if(typeof d%s===\"string\")", prop)
                    ("util.base64.decode(d%s,m%s=util.newBuffer(util.base64.length(d%s)),0)", prop, prop, prop)
                ("else if(d%s.length)", prop)
                    ("m%s=d%s", prop, prop);

This PR switch from passing a Buffer (the else branch in the snippet above) to passing a base64 encoded string (the if branch in the snippet above).

Encoding/Decoding a non empty buffer was already tested and I added a test for encoding/decoding an empty buffer. As expected the test fails with the current code:

  1) Datastore
       create, retrieve and delete
         should save/get/delete an empty buffer:
     Error: 3 INVALID_ARGUMENT: The value "buf" does not contain a value.

I am not sure if #755 should be marked as fixed or if we should wait for protobufs to be fixed ?

[codecov]

Codecov Report

Merging #767 (398b614) into master (96ecdfa) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #767   +/-   ##
=======================================
  Coverage   98.94%   98.94%           
=======================================
  Files          11       11           
  Lines        7893     7896    +3     
  Branches      469      469           
=======================================
+ Hits         7810     7813    +3     
  Misses         81       81           
  Partials        2        2           

Impacted Files	Coverage Δ
src/entity.ts	100.00% <100.00%> (ø)

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[crwilcox]

Thanks for the contribution!

[vicb]

Thanks for merging the PR Chris.