TypeError: Cannot read property 'observe' of undefined

[macsftech]

I'm getting this error:
TypeError: Cannot read property 'observe' of undefined

This is my implementation:

[ayrtonlacerda]

the same issue

[ftaibi]

same issue

[ricardo-0x07]

same issue

[LucasESchuster]

did you find out how to resolve this?

[etornam45]

I also have same issue

[etornam45]

I've solved mine, I just deleted all previous data in the collection and try again without changing the code