[5.4] Null return in a model relation with a id=0 key in DB table

[neoteknic]

• Laravel Version: 5.4.6
• PHP Version: 7.1.1
• Database Driver & Version: MariaDB 10.1.20

Description:

Eloquent relation return null instead of model when the id key in the database table is 0 (for non auto-increment table), it works fine in 5.2/5.3.

Steps To Reproduce:

Use a relation like belongTo in a model, submodel have key like id 0,1,2 if key = 0 the relation return null instead of returning the submodel .

[ntzm]

#17668

[neoteknic]

Fixed in #17668