feat(graphql-client): throw a descriptive error

[NickBolles]

This is a proposal for how to throw messages..

Before, data would be undefined and we would try to access the result field on data resulting in the following message:

  ● Accounts (e2e) › AccountsJS Client › when logged in › should login

    TypeError: Cannot read property 'tokens' of null

      at AccountsClient.<anonymous> (node_modules/@accounts/client/src/accounts-client.ts:97:35)
      at step (node_modules/tslib/tslib.js:136:27)
      at Object.next (node_modules/tslib/tslib.js:117:57)
      at fulfilled (node_modules/tslib/tslib.js:107:62)

After the change you get this message:

  ● Accounts (e2e) › AccountsJS Client › when logged in › should login

    GraphQLErrorList - 1 error in mutation: 
     mutation ($serviceName: String!, $params: AuthenticateParamsInput!) {
      authenticate(serviceName: $serviceName, params: $params) {
        sessionId
        tokens {
          refreshToken
          accessToken
        }
      }
    }
        - User not found

Close #823

[NickBolles]

I also added a fix for the following error:

   GraphQLErrorList - 1 errors in mutation: 
     mutation impersonate($accessToken: String!, $username: String!) {
      impersonate(accessToken: $accessToken, username: $username) {
        authorized
        tokens {
          refreshToken
          accessToken
        }
        user {
          id
          email
          username
        }
      }
    }

        - Cannot query field "email" on type "User". Did you mean "emails"?

[pradel]

@NickBolles that's a good idea and a better behavior thanks for this 👍
I am just wondering if it would be better to use the default GraphqlError object?

[NickBolles]

@pradel it looks like there's a potential to have multiple errors, and it's not possible to throw multiple errors, so I made a wrapper for it and let the consumer have access to the raw list of errors via the errors property. I'm up for figuring out a better way though!

[NickBolles]

@pradel should we check if there's only one error and throw that error by itself, otherwise throw the errorList?

[pradel]

@NickBolles I think it's fine that way :) do you think you could add an example of how to handle the error in the graphql documentation? website/docs/transports/graphql.md

[NickBolles]

sorry that took so long, I didn't see your response till now. Just added a little blurb about it. Let me know if you think it needs any changes.

While I was at it I updated the example to be more accurate (at least in my experience)

[ducan-ne]

cool

[pradel]

@NickBolles sorry I didn't get back to it earlier. Can you please resolve the conflicts you have so I can merge it? :)

[NickBolles]

@pradel done!

[pradel]

@NickBolles looks like the tests are failing, can you please take a look?

[NickBolles]

@pradel that should be fixed now. Sorry for the huge delay

[pradel]

Thank you @NickBolles!