Implement 'FromForm' for 'Option' and 'Result'.

CHANGELOG.md

@@ -46,6 +46,8 @@ This release includes the following new features:
   * Quoted string, array, and table  based [configuration parameters] can be set
     via environment variables.
   * Log coloring is disabled when `stdout` is not a TTY.
+  * [`FromForm`] is implemented for `Option<T: FromForm>`, `Result<T: FromForm,
+    T::Error>`.
 
 [Fairings]: #FIXME
 [Native TLS support]: #FIXME

lib/src/request/form/from_form.rs

@@ -124,3 +124,21 @@ impl<'f> FromForm<'f> for &'f str {
         Ok(items.inner_str())
     }
 }
+
+impl<'f, T: FromForm<'f>> FromForm<'f> for Option<T> {
+    type Error = !;
+
+    #[inline]
+    fn from_form(items: &mut FormItems<'f>, strict: bool) -> Result<Option<T>, !> {
+        Ok(T::from_form(items, strict).ok())
+    }
+}
+
+impl<'f, T: FromForm<'f>> FromForm<'f> for Result<T, T::Error> {
+    type Error = !;
+
+    #[inline]
+    fn from_form(items: &mut FormItems<'f>, strict: bool) -> Result<Self, !> {
+        Ok(T::from_form(items, strict))
+    }
+}