Translation errors when parser returns null

[aleksandar-kandzhichki]

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[ ] feature request

Current behavior
When we provide custom TranslateParser, the translation get function errors if our parser returns null.

I have traced this down to this line of code:

core/projects/ngx-translate/core/src/lib/translate.service.ts

Line 355 in 920b95d

return typeof res !== "undefined" ? res : key;

Here, if we get null, since typeof null == "object" we return res - which is null, and then in

core/projects/ngx-translate/core/src/lib/translate.service.ts

Line 387 in 920b95d

if (typeof res.subscribe === "function") {

we get null.subscribe which produces the error
So maybe it could be compared with null too

Expected/desired behavior
Probably the translator should treat it same as undefined - return the key

Reproduction of the problem
create translation with some key and value null e.g.
{
"mytranslation": null
}
and use parser that simply returns the value of "mytranslation"

What is the motivation / use case for changing the behavior?
better quality

Please tell us about your environment:

• @ngx-translate/core: "^10.0.2",
• @angular/core: "^6.0.3",
• browser: all
• language: typescript es6