RUST-806 Allow conversion of Options to Bson types

Author: NBSquare

src/bson.rs

@@ -304,6 +304,18 @@ impl From<DbPointer> for Bson {
     }
 }
 
+impl<T> From<Option<T>> for Bson
+where
+    T: Into<Bson>,
+{
+    fn from(a: Option<T>) -> Bson {
+        match a {
+            None => Bson::Null,
+            Some(t) => t.into(),
+        }
+    }
+}
+
 /// This will create the [relaxed Extended JSON v2](https://docs.mongodb.com/manual/reference/mongodb-extended-json/) representation of the provided [`Bson`](../enum.Bson.html).
 impl From<Bson> for Value {
     fn from(bson: Bson) -> Self {

src/tests/modules/bson.rs

@@ -143,6 +143,17 @@ fn from_impls() {
         Bson::Document(doc! {"a": "b"})
     );
 
+    // Optionals
+    assert_eq!(Bson::from(Some(4)), Bson::Int32(4));
+    assert_eq!(
+        Bson::from(Some(String::from("data"))),
+        Bson::String(String::from("data"))
+    );
+    assert_eq!(Bson::from(None::<i32>), Bson::Null);
+    assert_eq!(Bson::from(None::<String>), Bson::Null);
+    assert_eq!(doc! {"x": Some(4)}, doc! {"x": 4});
+    assert_eq!(doc! {"x": None::<i32>}, doc! {"x": Bson::Null});
+
     let db_pointer = Bson::try_from(json!({
         "$dbPointer": {
             "$ref": "db.coll",