Report empty textdomains in i18n

[kkmuffme]

esc_html_e( 'foo', '' );

should be reported as an error, since the textdomain should not be empty (it can be, but in 99.99% of cases this is unwanted)
Same for __(), _x(),...

[jrfnl]

The I18n sniff will report this correctly - Mismatched text domain. Expected 'my-plugin' but got ''. - as soon as you either pass a text-domain via a custom ruleset or via the command-line.

This sniff is also used by WP Core and for WP Core, usage without a text-domain is valid and - as the $text_domain variable is optional with a default of '', using it like in the above code sample is too.

[kkmuffme]

Thx, had a mistake on our end not passing the textdomain correctly anymore

[jrfnl]

Looks like the default value for the $domain parameter is now 'default' instead of an empty string for nearly all translation functions.

This means that passing an empty string is no longer a valid action as it would overrule the default value for the parameter and make the text string untranslatable.