Empty-property scoped context does not affect term selection.

[gkellogg]

Adding a minimal/empty property-scoped context should not affect the using terms defined in outer context.

From w3c/wot-thing-description#894.

[davidlehn]

Perhaps also add an even more minimal test. Surprised this wasn't covered before.
in:

{
  "ex:title": "top",
  "ex:thing": {
    "ex:title": "sub"
  }
}

context:

{
  "@context": {
    "thing": {
      "@id": "ex:thing",
      "@context": {}
    },
    "title": "ex:title"
  }
}

out:

{
  "@context": {
    "thing": {
      "@id": "ex:thing",
      "@context": {}
    },
    "title": "ex:title"
  },
  "title": "top",
  "thing": {
    "title": "sub"
  }
}

And while we're at it, how about a basic expand test that jsonld.js also is failing now. How was this also not covered?
in:

{
  "@context": {
    "thing": {
      "@id": "ex:thing",
      "@context": {}
    },
    "title": "ex:title"
  },
  "title": "top",
  "thing": {
    "title": "sub"
  }
}

out:

[
  {
    "ex:title": [
      {
        "@value": "top"
      }
    ],
    "ex:thing": [
      {
        "ex:title": [
          {
            "@value": "sub"
          }
        ]
      }
    ]
  }
]

[davidlehn]

This is named with "minimal/empty" contexts, but in the case of jsonld.js, I think any non-null context data fails. This may be a general additive context issue.