Serializer plugin does not store the initial values when incrementing/decrementing values

[boesing]

Bug Report

Q	A
Version(s)	2.11.1

Summary

Given the AbstractCommonAdapterTest::testIncrementItemInitialValue and AbstractCommonAdapterTest::testDecrementItemInitialValue, the adapter has to treat non-existent values as 0 when using increment or decrement methods.

Current behavior

When using the Serializer plugin, increment and decrement will immediately stop due to the plugin stopping the propagation of the event.

How to reproduce

There are existing unit tests which are already failing within the AbstractCommonAdapterTest.

public function testDecrementItemInitialValue(): void
{
    $this->assertEquals(-5, $this->storage->decrementItem('counter', 5));
    $this->assertEquals(-5, $this->storage->getItem('counter'));
}

public function testIncrementItemInitialValue(): void
{
    $this->assertEquals(5, $this->storage->incrementItem('counter', 5));
    $this->assertEquals(5, $this->storage->getItem('counter'));
}

Both tests have to be executed with adapters implementing the Serializer plugin.

Expected behavior

Tests are passing.

[boesing]

Closed with #135