Remove mediaQuery declaration as an empty string in sizeConfig

[Fawke]

Type of issue

Bug

Description

Under the current design (as of v3.x), a publisher can declare mediaQuery string as empty in global sizeConfig object.

The implication of this is inconsistent behaviour when a publisher chooses to declare mediaQuery as an empty string, the current implementation may choose wrong Ad size for a given viewport size. For details and an example, click here.

Related - #4691

A fix could be to completely block empty mediaQuery string declaration. Since this solution could be a breaking change for some publishers who're already using empty mediaQuery declaration in sizeConfig, the change should go in the next major release.

[gglas]

@Fawke hey Neelanjen -- did 4691 resolve this issue and we can close it out?

[Fawke]

@gglas Hi Gareth - No, we didn't resolve this issue in #4691. It was a breaking change, so @mkendall07 suggested the change should go out as part of a next major release. It was supposed to be 4.0, but that didn't happen. We can include in now, in 5.0. It's a small edge case in the core sizesMapping module which can lead to some unexpected behaviour.

[patmmccann]

Closing with the merge to 5