Fix panic from not checking for nil (#19)

* Fix panic from not checking for nil

* add fmt package

session/session.go

@@ -1,6 +1,8 @@
 package session
 
 import (
+	"fmt"
+
 	"github.com/gorilla/context"
 	"github.com/gorilla/sessions"
 	"github.com/labstack/echo/v4"
@@ -32,7 +34,11 @@ var (
 
 // Get returns a named session.
 func Get(name string, c echo.Context) (*sessions.Session, error) {
-	store := c.Get(key).(sessions.Store)
+	s := c.Get(key)
+	if s == nil {
+		return nil, fmt.Errorf("%q session not found", name)
+	}
+	store := s.(sessions.Store)
 	return store.Get(c.Request(), name)
 }