fix: normalize null to undefined in ElicitResultSchema content field

Add z.preprocess to convert null values to undefined in the content field of ElicitResultSchema for better leniency while maintaining type compatibility. Per MCP spec, content is typically omitted for decline/cancel actions.

Author: mattzcarey

src/types.ts

@@ -1831,8 +1831,13 @@ export const ElicitResultSchema = ResultSchema.extend({
     /**
      * The submitted form data, only present when action is "accept".
      * Contains values matching the requested schema.
+     * Per MCP spec, content is "typically omitted" for decline/cancel actions.
+     * We normalize null to undefined for leniency while maintaining type compatibility.
      */
-    content: z.record(z.string(), z.union([z.string(), z.number(), z.boolean(), z.array(z.string())])).optional()
+    content: z.preprocess(
+        (val) => (val === null ? undefined : val),
+        z.record(z.string(), z.union([z.string(), z.number(), z.boolean(), z.array(z.string())])).optional()
+    )
 });
 
 /* Autocomplete */