Werk #11903: Fix crash in hearbeat CRM general

Component	Checks & agents
Title	Fix crash in hearbeat CRM general
Date	Feb 1, 2021
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.1.0b1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 2.0.0b6 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 1.6.0p21 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

Fix cases where the Heartbeat CRM would crash with a TypeError.

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