Just to be more complete than the accepted answer: the syntax for refspec is [+][src][:dst], and not more than one of srcand is :dstomitted (so the empty line and +by themselves are both invalid).
Therefore, the syntax is not --forcefor your case - +local:remoteand not local:+remote.
--force + refspec, .. :
git push --force origin someBranch local:remote anotherBranch
git push origin +someBranch +local:remote +anotherBranch