Swift-311 Make ReadPrefrerence getters return non-optionals (#279)

Author: ncarbon

Sources/MongoSwift/MongoClient.swift

@@ -142,7 +142,7 @@ public class MongoClient {
     }
 
     /// The `ReadPreference` set on this client
-    public var readPreference: ReadPreference? {
+    public var readPreference: ReadPreference {
         return ReadPreference(from: mongoc_client_get_read_prefs(self._client))
     }
 

Sources/MongoSwift/MongoCollection.swift

@@ -39,7 +39,7 @@ public class MongoCollection<T: Codable> {
     }
 
     /// The `ReadPreference` set on this collection.
-    public var readPreference: ReadPreference? {
+    public var readPreference: ReadPreference {
         return ReadPreference(from: mongoc_collection_get_read_prefs(self._collection))
     }
 

Sources/MongoSwift/MongoDatabase.swift

@@ -85,7 +85,7 @@ public class MongoDatabase {
     }
 
     /// The `ReadPreference` set on this database
-    public var readPreference: ReadPreference? {
+    public var readPreference: ReadPreference {
         return ReadPreference(from: mongoc_database_get_read_prefs(self._database))
     }