Collection: new widget to add book to collection

internal/myvalidator/myvalidator.go

@@ -57,6 +57,9 @@ func ReturnErrorsAsJsonResponse(ac *appcontext.AppContext, err error) {
 		ac.C.JSON(httpError.StatusCode, gin.H{"error": httpError.Err.Error()})
 		return
 	}
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		ac.C.JSON(http.StatusNotFound, gin.H{"error": err.Error()})
+	}
 	ac.C.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 }