fix(@types/select): When value is mandatory & multiple false, value can be null

Author: gristow

packages/svelte-materialify/@types/Select.d.ts

@@ -9,7 +9,7 @@ interface SelectProps {
    * Value of the select. 
    * If multiple is true, this will be an array; otherwise a single value.
    */
-  value?: (number[] | string[]) | number | string;
+  value?: number[] | string[] | number | string | null;
   /** List of items to select from. */
   items?: { name: string | number, value: string | number }[];
   /** Whether select is the `filled` material design variant. */