Fix null handling for localToDate in TreeMapper Export component

[coderabbitai]

Problem

The localToDate state variable in src/features/user/TreeMapper/Analytics/components/Export/index.tsx was changed from Date to Date | null but the code doesn't handle null values properly.

Issues to address

1. Filename formatting: The saveAs function uses format(localToDate, 'dd-MMM-yy') which will throw an error if localToDate is null
2. API request body: The export request body includes endDate: localToDate which may need null handling depending on API requirements

Suggested fixes

1. Add conditional check before formatting: localToDate ? format(localToDate, 'dd-MMM-yy') : 'no-date'
2. Handle null values in API request body appropriately

References

• PR: refactor(tree-mapper): replace color codes with design system color c… #2592
• Comment: refactor(tree-mapper): replace color codes with design system color c… #2592 (comment)
• Requested by: @mohitb35