TypeError: Cannot read property 'push' of null

[DanteParticipant]

TypeError: Cannot read property ‘push’ of null
at ActivityService.webpackJsonp.114.ActivityService.addActivity (http://localhost:8100/build/main.js:319:48)
at MapSubscriber.project (http://localhost:8100/build/main.js:2454:51)
at MapSubscriber._next (http://localhost:8100/build/vendor.js:61997:35)
at MapSubscriber.Subscriber.next (http://localhost:8100/build/vendor.js:25812:18)
at XMLHttpRequest.onLoad (http://localhost:8100/build/vendor.js:39650:38)
at t.invokeTask (http://localhost:8100/build/polyfills.js:3:15660)
at Object.onInvokeTask (http://localhost:8100/build/vendor.js:5126:33)
at t.invokeTask (http://localhost:8100/build/polyfills.js:3:15581)
at r.runTask (http://localhost:8100/build/polyfills.js:3:10834)
at e.invokeTask [as invoke] (http://localhost:8100/build/polyfills.js:3:16794)

[DanteParticipant]

while trying to get in unit in web browser face this
how solve

[Author]

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