fhir_search returns `entry: [ ]` (an empty array) if search query doesn't return any results which is not valid according to fhir documentation

[bartek-sarul]

Steps to reproduce:

select fhir_search('{"resourceType":"Patient", "queryString":"identifier=SOME_NON_EXISTING_IDENTIFIER"}');

This returns

{
  "resourceType":"Bundle",
  "type":"searchset",
  "total":0,
  "link":[{
    "relation":"self",
    "url":"Patient/search?identifier=SOME_NON_EXISTING_IDENTIFIER&_page=0"
  }],
  "entry":[]
}

According to fhir documentation https://www.hl7.org/fhir/json.html

Objects are never empty. If an element is present in the resource, it SHALL have properties as defined for its type, or 1 or more extensions

String property values can never be empty. Either the property is absent, or it is present with at least one character of content

This has also been confirmed on fhir implementers chat https://chat.fhir.org/#narrow/stream/implementers/topic/returning.20search.20bundle.20with.20no.20result

Empty elements (arrays or strings) are not permitted.

Expected result:

{
  "resourceType":"Bundle",
  "type":"searchset",
  "total":0,
  "link":[{
    "relation":"self",
    "url":"Patient/search?identifier=SOME_NON_EXISTING_IDENTIFIER&_page=0"
  }]
}