Werk #18374: Fix Alternative valuespec crash when switching between incompatible types

Component

Setup

Title

Fix Alternative valuespec crash when switching between incompatible types

Date

Mar 4, 2026

Level

Trivial Change

Class

Bug Fix

Compatibility

Compatible - no manual interaction needed

Checkmk versions & editions

2.6.0b1 Not yet released	Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME)
2.5.0b1 Not yet released	Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME)

When switching between alternatives in a form (e.g. from an SNMPv3 tuple to an SNMPv2c string), the stored value may not match the newly selected alternative's expected type. Previously, this caused an AttributeError in most scenarios.

The fix now uses the alternative's default_value() when the stored value's type does not match the selected alternative, preventing the crash.

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