Resolve "problem with projects validation"

Closes #290 (closed)

src/models/disease.ts

@@ -2,7 +2,7 @@ import { z } from 'zod';
 
 export const disease = z.object({
   id: z.number().int().positive(),
-  link: z.string().optional(),
+  link: z.string().nullable(),
   type: z.string(),
   resource: z.string(),
   annotatorClassName: z.string(),