Actually the fact that they got the warrant is a statement by the judge that the warrant is valid. Or at least he believed so
and exactly which law is that
they ever 'prosecuted' anything. They tried to argue Shield Law but that is about protecting a source which was not applicable in this case because no one had to ask him for his source when he himself had possession of the prototype and he himself took the photos etc (by his own admission)
The warrant etc was about the criminal act of buying stolen property (stolen as defined by California's failure to return laws), which Chen also confessed to via his bragging in the articles.
I'm not going to get into a long discussion about this, so I'll deal with it briefly.
Bloggers are journalists under Californian law. If Police want information from a journalist, they must subpoena it, this is the shield law.
No charges have been laid, this was a fishing expedition, precisely what the shield law is designed to prevent. Police have said they they were investigating whether a crime has been committed, so what seems cut-and-dried to you must elude them (??) Maybe it's just not as straightforward as it seems to you.
A judge allowed the warrant, but this was contested, which is proper and legal, but rather than follow through with their own system, the 'independent' judge refused to rule, passed it back to the original judge, who cannot review his own decision and the police withdrew the warrant. Hence my comment about the legal system failing to follow its own rules and covering a bad decision by taking the warrant off the table.
Fact is, the damage has been done, shield law broken, and police gained leverage over Chen by illegal means.
It has been contended here that the warrant hasn't been ruled illegal, but the courts refused to submit it to the proper test of the law. Their refusal speaks louder than words. If you or I tried to refuse to participate in the legal process, you know where we would end up!