Can you explain what purpose of this code?

[spamnam]

Im trying to understad how $this->classCastCache array works in Model class. There are only two places in HasAttributes trait where you can add value to this array.

here:

    protected function getClassCastableAttributeValue($key, $value)
    {
        if (isset($this->classCastCache[$key])) {
            return $this->classCastCache[$key];
        } else {
            $caster = $this->resolveCasterClass($key);

            $value = $caster instanceof CastsInboundAttributes
                        ? $value
                        : $caster->get($this, $key, $value, $this->attributes);

            if ($caster instanceof CastsInboundAttributes || ! is_object($value)) {
                unset($this->classCastCache[$key]);
            } else {
                $this->classCastCache[$key] = $value;
            }

            return $value;
        }
    }

and here:

   protected function setClassCastableAttribute($key, $value)
    {
        $caster = $this->resolveCasterClass($key);

        if (is_null($value)) {
            $this->attributes = array_merge($this->attributes, array_map(
                function () {
                },
                $this->normalizeCastClassResponse($key, $caster->set(
                    $this, $key, $this->{$key}, $this->attributes
                ))
            ));
        } else {
            $this->attributes = array_merge(
                $this->attributes,
                $this->normalizeCastClassResponse($key, $caster->set(
                    $this, $key, $value, $this->attributes
                ))
            );
        }

        if ($caster instanceof CastsInboundAttributes || ! is_object($value)) {
            unset($this->classCastCache[$key]);
        } else {
            $this->classCastCache[$key] = $value;
        }
    }

As you see in both functions there are this construction:

            if ($caster instanceof CastsInboundAttributes || ! is_object($value)) {
                unset($this->classCastCache[$key]);
            } else {
                $this->classCastCache[$key] = $value;
            }

So only !$caster instanceof CastsInboundAttributes && is_object($value) can be added to this array. If so then why are we checking for this $caster instanceof CastsInboundAttributes || ! is_object($value) to unset entry THAT HAS 0 CHANCE of existensce?