Possible fix for #6710 - explicitly make auto_increment_prefix nullable (#6716)

* Possible fix for #6710 - explicitly make auto_increment_prefix nullable

* Added migration to make auto_increment_prefix explicitly nullable

database/migrations/2014_11_20_224421_add_prefix_to_settings.php

@@ -15,7 +15,7 @@ class AddPrefixToSettings extends Migration {
 		//
 		Schema::table('settings', function(Blueprint $table) {
 
-			$table->string('auto_increment_prefix')->default(0);
+			$table->string('auto_increment_prefix')->nullable()->default(NULL);
 
 		});
 	}

database/migrations/2019_02_14_154310_change_auto_increment_prefix_to_nullable.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class ChangeAutoIncrementPrefixToNullable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('settings', function (Blueprint $table) {
+            $table->boolean('auto_increment_prefix')->nullable()->default(null)->change();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        //
+    }
+}