fix(box): filter empty file IDs from sourceFileIds input

Add .filter(Boolean) after splitting sourceFileIds to prevent empty
strings from trailing/double commas being sent as invalid file IDs
to the Box Sign API.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: waleedlatif1

apps/sim/tools/box_sign/create_request.ts

@@ -127,7 +127,7 @@ export const boxSignCreateRequestTool: ToolConfig<BoxSignCreateRequestParams, Bo
       'Content-Type': 'application/json',
     }),
     body: (params) => {
-      const fileIds = params.sourceFileIds.split(',').map((id: string) => id.trim())
+      const fileIds = params.sourceFileIds.split(',').map((id: string) => id.trim()).filter(Boolean)
       const sourceFiles = fileIds.map((id: string) => ({ type: 'file', id }))
 
       const signers: Array<Record<string, unknown>> = [