struct Key: Codable, Hashable {
  var string: String
}
struct Value: Codable {
  var string: String
}
struct Context: Codable {
  var dictionary: [Key: Value] = [:]
}

let encoded = try JSONEncoder().encode([Context(dictionary: [Key(string: "..."): Value(string: "...")])])
print(String(data: encoded, encoding: .utf8))
// Optional("[{\"dictionary\":[{\"string\":\"...\"},{\"string\":\"...\"}]}]")
let decoded = try JSONDecoder().decode([Context].self, from: encoded)
print(decoded)
// ✓ Works just fine.

let emptyEncoded = try JSONEncoder().encode([Context()])
print(String(data: emptyEncoded, encoding: .utf8))
// Optional("[{\"dictionary\":{}}]")
let emptyDecoded = try JSONDecoder().decode([Context].self, from: emptyEncoded)
print(emptyDecoded)
// ✗ Throws: “typeMismatch(Swift.Array<Foundation.JSONValue>, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "dictionary", intValue: nil)], debugDescription: "Expected to decode Array<JSONValue> but found a dictionary instead.", underlyingError: nil))”