migrations/2017_01_15_000000_make_table_name_nullable_in_permissions_table.php
public function up()
    {
        Schema::table('permissions', function (Blueprint $table) {
            $table->string('table_name')->nullable()->default(null)->change();
        });
    }
public function up()
    {
        Schema::table('permissions', function (Blueprint $table) {
            $table->string('table_name')->nullable()->default(null)->change();
        });
    }
Run the migrations.

@return void