title: How to NOT serialize default values
body: <p>I can't help to look at my very empty pockets and wonder if there's any penny I could pinch in my web app.<br>
  Looking at the JSON I've been spitting out, I can't help to wonder if there's a way to NOT serialize default values, eg:</p>
  
  <pre><code>{
  "gservs": {
    "EmpresaId": 1044,
    "GservsId": 7,
    "Descricao": "Cabelos"
  },
  "EmpresaId": 1044,
  "ServicosId": 97,
  "GServsId": 7,
  "Descricao": "auxiliar geral",
  "Informativo": "",
  "simNao": false,
  "PermiteEncaixe": false,
  "UsaQuimica": false,
  "CustosGerais": 0.0000,
  "Preco": 0.0000,
  "Comissao": 0.0000,
  "ValPercComissao": "P",
  "TipoComissao": false,
  "ValPercCustos": "P",
  "TipoCusto": false,
  "ServicoAux": true,
  "ValPercComisAux": "P",
  "TipoComissaoAux": false,
  "IncidComisAux": "A",
  "DiasRetorno": 0,
  "TempoExecucao": "00:00:00",
  "TempoHora": 0,
  "TempoMinMarcacao": 0,
  "TempoHoraMarcacao": 0,
  "TempoMin": 0,
  "Ativo": false,
  "Mobilidade": false,
  "PermiteSimultaneidade": false,
  "ParticipaMilhagem": true
  }
  </code></pre>
  
  <p>If you check this out, you can count 406 bytes were wasted with default values. My estimate is that at the end of a regular day, I will have wasted about 1 dollar (I'm in Azure Zone 3 - Brazil South) with wasted bandwidth...</p>
  
  <p>I learned a while back that I can tell JsonSerializer to ignore <code>null</code>s properties, so, can I do the same to "default" values as well?</p>