Fix null id in arguments

[Aschen]

What does this PR do?

This PR prevent to add null or undefined arguments to the query args in http protocol.

Fix #324

How should this be manually tested?

Run this snippet at the root of sdk-javascript folder, the document id should not be the string 'null':

const Kuzzle = require('./index').Kuzzle;

const kuzzle = new Kuzzle('http', { host: 'localhost', port: 7512 });

(async () => {
  try {
    await kuzzle.connect()
    await kuzzle.index.create('index');
    await kuzzle.collection.create('index', 'collection');

    const doc = await kuzzle.document.create(
      'index',
      'collection',
      null,
      { hello: 'world' },
      { refresh: 'wait_for' }
    );
    console.log(doc);

    const document = await kuzzle.document.get('index', 'collection', doc._id);

    console.log(document);
  } catch (error) {
    console.log(error);
  }
})()

[codecov-io]

Codecov Report

Merging #330 into 6-dev will increase coverage by <.01%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           6-dev    #330      +/-   ##
========================================
+ Coverage   97.5%   97.5%   +<.01%     
========================================
  Files         28      28              
  Lines       1404    1405       +1     
========================================
+ Hits        1369    1370       +1     
  Misses        35      35

Impacted Files	Coverage Δ
src/networkWrapper/protocols/http.js	88.23% <100%> (+0.14%)	⬆️

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