text: Title: Error making request when request has no body and there is a `report::hide_request::body` configuration.
  Body: ## Bug report
  
  ### Environment
  - Operating System: Mac OS
  - ScanAPI version: 2.3.0
  
  ### Description of the bug 
  Error making request when request has no body and there is a `report::hide_request::body` configuration.
  
  
  ```shell
  ▶ scanapi run
  Loading file ./scanapi.conf
  Loading file scanapi.yaml
  Writing documentation
  Making request GET http://demo.scanapi.dev/api/v1/health/
  
  Error to make request `http://demo.scanapi.dev/api/v1/health/`.
  the JSON object must be str, bytes or bytearray, not 'NoneType'
  
  Making request POST http://demo.scanapi.dev/api/v1/rest-auth/login/
  
  The documentation was generated successfully.
  It is available at /Users/camilamaia/workspace/scanapi-org/test-tutorial/scanapi-report.html
  ```
  
  ![image](https://user-images.githubusercontent.com/2728804/121076386-bc286b80-c7ac-11eb-9918-908ed4660abc.png)
  
  ### Expected behavior ?
  Health request to appear in the report
  
  ### How to reproduce the the bug ?
  specification file `scanapi.yaml`:
  
  ```yaml
  endpoints:
    - name: snippets-api
      path: http://demo.scanapi.dev/api/v1/
      headers:
        Content-Type: application/json
      requests:
        - name: health
          method: get
          path: /health/
          tests:
            - name: status_code_is_200
              assert: ${{ response.status_code == 200 }}
            - name: body_equals_ok
              assert: ${{ response.json() == "OK!" }}
        - name: get_token
          path: /rest-auth/login/
          method: post
          body:
            username: ${USER}
            password: ${PASSWORD}
  ```
  
  Configuration file `scanapi.conf`:
  
  ```yaml
  report:
    hide_request:
      body:
        - password
    hide_response:
      body:
        - key
  ```