Prevent duplicate user entries by handling empty emails

Fixes an issue where creating or editing users with empty email fields would violate a unique constraint in the database. The solution involves updating user routes to treat empty email strings as NULL, adjusting validation schemas, and providing a script to clean existing data.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: a8a78c07-e900-425c-a577-5b4c5894379d
Replit-Commit-Checkpoint-Type: full_checkpoint
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replit.md

@@ -139,4 +139,14 @@ Preferred communication style: Simple, everyday language.
 - **Issue**: Admin password changes failed in production with ERR_MODULE_NOT_FOUND for localAuth.production
 - **Root Cause**: Dynamic imports in production needed `.js` extension for compiled files
 - **Solution**: Updated import paths to use `./localAuth.production.js` for production environment
-- **Result**: Password hashing now works correctly in production for user updates
+- **Result**: Password hashing now works correctly in production for user updates
+
+#### Email Constraint Fix for User Management
+- **Issue**: Both user creation and editing failed with "duplicate key value violates unique constraint users_email_key" error
+- **Root Cause**: PostgreSQL treats empty strings (`""`) as unique values, but multiple users with empty emails violated uniqueness constraint
+- **Solution Implemented**:
+  - Updated both POST `/api/users` (creation) and PUT `/api/users/:id` (editing) routes to convert empty emails to `NULL`
+  - Enhanced validation schemas to accept `null` values for email fields
+  - Created `fix-duplicate-empty-email.sql` script to clean existing database records
+  - Improved error handling and logging for better production debugging
+- **Result**: Users can now be created and edited with optional email fields without constraint violations