[BUG] pd dev fails on some sources: "Cannot return null for non-nullable field Selectable.label"

**Describe the bug**
When I run `pd dev` on a Webflow source with a webflow app prop, I get the error:
```
Configuring prop webflow...
panic: graphql: Cannot return null for non-nullable field Selectable.label

goroutine 61 [running]:
pd/core.determineAppAuthProvisionID(0xc00032e774, 0x7, 0xc00032e77b, 0x3, 0x0, 0xc00032e790, 0x7, 0x0, 0x0, 0x0, ...)
/home/runner/work/pipedreamin/pipedreamin/cli/core/configure_props.go:54 +0x2d1
pd/core.configureAppProp(0xc00032e774, 0x7, 0xc00032e77b, 0x3, 0x0, 0xc00032e790, 0x7, 0x0, 0x0, 0x0, ...)
/home/runner/work/pipedreamin/pipedreamin/cli/core/configure_props.go:152 +0x1b5
```

**To Reproduce**
Steps to reproduce the behavior:
1. Go to https://pipedream.com/accounts
2. Connect a Webflow account
3. From the root of the pipedream repo, run the [CLI](https://pipedream.com/docs/cli/reference/) command:
```
pd dev components/webflow/sources/site-published/site-published.js
```
4. See error

**Expected behavior**
The CLI shows a list of Webflow accounts to select from.

**Screenshots**

**Additional context**
The error seems to occur when a connected account is missing an [“identity”](https://user-images.githubusercontent.com/19861096/162022979-af8867b3-11cb-4295-ab6b-a27725ec7e2f.png) or “nickname” to use as an option label in the CLI. The _UI_ uses/displays the app name by default, as the nickname, when a nickname isn’t explicitly set. The CLI _doesn’t_ use the app name as the account label (e.g. in the options list for the `webflow` prop) by default, and expects the account label to be non-null.
Slack thread: https://pipedream-users.slack.com/archives/C01E5KCTR16/p1648840118427189