What is the per se reversible error rule?

[27 Cal.3d 528] The theory behind the per se reversible error rule was stated as follows: ". . . where the accused is not legally committed within the meaning of section 995 of the Penal Code, the commitment is voidable. Upon proper objection, the superior court has no jurisdiction to proceed. It is the same as if no preliminary examination at all had been held, and is analogous to the situation where no evidence to connect the accused with the crime is introduced at the preliminary examination. In such event, of course, the information must be quashed. (Greenberg v. Superior Court, 19 Cal.2d 319 (121 P.2d 713).)"