Angular 5 or 6 subscriptions don’t work when using proxy - angular5

Question

I have built a Java Restful API and I want to access it from Angular 5. For development i have angular server running on port 4200 while my backend runs on 8080. I am trying to setup proxy in angular in order to communicate with backend.
So i have created the following proxy.conf.json file:
{
"/**": {
"target": "http://localhost:8080",
"changeOrigin": true,
"secure": false,
"logLevel": "debug"
}
}
Then i run in terminal
ng serve --proxy-conf proxy.conf.json
and i get the message
Proxy created: /** -> http://localhost:8080
[HPM] Subscribed to http-proxy events: [ 'error', 'close' ]
So till now everything is fine.
When i type in browser url for example
http://localhost:4200/incidents/all
everything works fine and i get the response
[{"id":55,"protocolNo":121212222,"date":1525122000000,"isPayed":true,"yliko":"fdasdfasfsaf","makro":"fdsa","anoso":"fdsa","mikro":"fdsafds","symperasma":"dfsdfsadf","klinikesPlirofories":"fsdafds","histo":"dfsadffga","simpliromatikiEkthesi":"fdsadfsdfa","patient":{"id":1,"firstName":"Μιχαήλ","lastName":"Τουτουδάκης","birthday":"1975-08-19","fatherName":"Δημήτριος","telephone":"6948571893","email":"mixtou#gmail.com","sex":true,"city":{"id":1,"name":"Χανιά"}},"doctor":{"id":1,"firstName":"όνομα","lastName":"επίθετο","telephone":"2821074737","email":"papa#papa.com","fatherName":"πατέρας","specialty":{"id":1,"name":"Αγγειοχειρουργική"},"city":{"id":1,"name":"Χανιά"}},"clinic":{"id":1,"name":"Κλινική Τσεπέτη","telephone":"123456789","address":"Παπαναστασίου","email":"test#test.com"},"signingDoctor":{"id":1,"lastName":"Δασκαλάκη","firstName":"Άννα"},"mikroskopikaSymperasma":null,"anosoEkthesi":null,"cancer":true},{"id":56,"protocolNo":11111,"date":1525640400000,"isPayed":false,"yliko":"dfsadfs","makro":"dfsfsdfdsdfsadfsa","anoso":"dfsdfsfdssfafasd","mikro":"dsfdfsadfsadfssdf","symperasma":"σδγσδγσαδγσγσασδγ","klinikesPlirofories":"δδφφγφγαφαγ","histo":"fdsasdfd","simpliromatikiEkthesi":"γαγσαδσγσδγσδαγ","patient":{"id":5,"firstName":"Στέφανος","lastName":"Μαριόλος","birthday":"2018-03-26","fatherName":"","telephone":"4838583845","email":"","sex":true,"city":{"id":2,"name":"Ρέθυμνο"}},"doctor":{"id":3,"firstName":"Χαράλαμπος","lastName":"Πρωτοπαπαδάκης","telephone":"4343454345","email":"","fatherName":"","specialty":{"id":29,"name":"Πνευμονολογία - Φυματιολογία"},"city":{"id":1,"name":"Χανιά"}},"clinic":{"id":1,"name":"Κλινική Τσεπέτη","telephone":"123456789","address":"Παπαναστασίου","email":"test#test.com"},"signingDoctor":{"id":1,"lastName":"Δασκαλάκη","firstName":"Άννα"},"mikroskopikaSymperasma":"γσαγδσασαδγδασγαγσγσ","anosoEkthesi":"φδαφγφγφδσγ","cancer":true}]
However visiting backend end point from angular i get nothing.
For incidents for example i have the following service:
getIncidents(): Observable<Incident[]> {
console.log('getting incidents');
const incidentsUrl = '/incidents/all';
return this.http.get<Incident[]>(incidentsUrl)
.pipe(catchError(ErrorHandler.handleError));
}
Which generates the following error in javascript console:
core.js:1440 ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'push' of undefined
TypeError: Cannot read property 'push' of undefined
At the following line:
this.subscriptions.push(this.incidentsService.getIncidents().subscribe((results) => {
this.comService.sendIncidents(results);
this.spinner.hide();
}));
Which means that this.incidentsService.getIncidents() retturns nothing??
Any Ideas??

Answer 1

I removed the this.subscriptions.push(...) action and everything works fine. Why is this happening when using subscriptions. I need them because onDestroy i call subscription.unsubsribe() to avoid memory leaks.
Note that this happens when using proxy. If i don't use proxy and deploy the project to tomcat everything works ok. I don't get null inside push().
Any Ideas???
The problem was at the declaration of subscriptions. In the beginning it was:
subscriptions: Subscription[];
I changed it to
subscriptions: Subscription[] = [];
and everything worked fine.
subscriptions
wasn't initialized.