problem

JS Exception: Cannot read property 'isEntity' of undefined

trace

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the following JS exception is triggered:
Cannot read property 'isEntity' of undefined
in constructor.doEnsureVisible @ ext-all-debug.js:200168:55

causes

TRANSLATE-2484 Buffered grid "ensure visible" override

Stack:
constructor.doEnsureVisible	@ ext-all-debug.js:200168:55
constructor.ensureVisible	@ ext-all-debug.js:199744:14
constructor.activateCell	@ ext-all-debug.js:205847:32
constructor.resumeActionableMode	@ ext-all-debug.js:205952:20
[anonymous]	@ ext-all-debug.js:205637:28
constructor.onRemove	@ ext-all-debug.js:182077:17
constructor.callParent	@ ext-all-debug.js:12493:32
constructor.onRemove	@ ext-all-debug.js:205572:16
constructor.fire	@ ext-all-debug.js:20731:42
constructor.doFireEvent	@ ext-all-debug.js:21700:47