It hasn't been released so we have no idea if it is actually nothing or not.
There is no possible way for the entire report to be released, and they all know it. There will be entire chapters redacted from Grand Jury testimonies, classified information, sources and methods, Executive Privilege, and everything about anyone that was not indicted. It is illegal. They just want to continue the game by saying they are hiding the truth.
There is a reason Bill Barr would not allow Rod Rosenstein to resign before the report was finished. Rod Rosenstein appointed Robert Mueller to head the special council after he himself signed off on FISA search warrants, which began this entire hoax. Barr wanted Rosenstein's signature on the document exonerating Trump of all of this... most likely, trying to save his own skin.
Though it is strange that McConnell would block the resolution to release the full report if it were truly nothing...
Congress has no power over what is released... but it would be smart to release as much as possible, because it will be leaked. McConnell only wants to keep control of what happens in the Senate... he's in charge there.
If Trump is guilt free show us the darn thing so we can know.
You have the Special Council for the US Department of Justice Robert Mueller, US Deputy Attorney General Rod Rosenstein, and US Attorney General William Barr, telling you Trump is guilt free and there was no criminal conspiracy or obstruction of justice. That's the highest authority there is. If that's not good enough for you then here's a box of Kleenex, and I guess you will not be voting for Trump in 2020.