Infinitive Phrase function

Look at the following example:

It is common to make mistakes.

Which function does this infinitive phrase have in the sentence?

In my opinion, it is not the subject (it). It is not an object (there is no object). It is not an object complement (there is no object). It is not a subject complement (common). It is not an adjective nor an adverb. I would appreciate any help.

Thanks.

Mauricio