public function up(): void 	{ 		Schema::create('referrals', function (Blueprint $table): void { 			$table->uuid('id')->primary(); 			$table->string('email')->unique(); 			$table->uuid('referrer_id'); 			$table->timestamp('resolved_at')->nullable(); 			$table->timestamps();  			$table->foreign('referrer_id')->references('id')->on('customers')->onDelete('cascade'); 		}); 	}