FIRST PROCESS

Steps ONE to reproduce the issue

Enable the plugin 'Captcha – ReCaptcha' following this process:
Menu 'Extensions' -> 'Plugin Manager' -> 'Captcha – ReCaptcha'
Then:
'Status' -> 'Enabled' -> 'Save'

Actual result

can't save the seting with the message:
Invalid field: Public Key
Invalid field: Private Key

As the fields are both required

SECOND PROCESS

Steps TWO to reproduce the issue

Then now Enable the same plugin 'Captcha – ReCaptcha' following this process:
Menu 'Extensions' -> 'Plugin Manager' -> enable 'Captcha – ReCaptcha' Status with the button

Actual result

Then the plugin is enable without having to complete the fields