Fix PRMMinimize behaviour on simple paren'ed expressions

data/15-regressions.blt

@@ -1059,3 +1059,10 @@ func = do
     stmt2
     )
     `shouldReturn` thing
+
+#golden minimize parens basic test
+-- brittany { lconfig_operatorParenthesisRefactorMode: PRMMinimize }
+func = func (abc) (def)
+#expected
+-- brittany { lconfig_operatorParenthesisRefactorMode: PRMMinimize }
+func = func abc def

source/library/Language/Haskell/Brittany/Internal/Components/OpTree.hs

@@ -185,6 +185,7 @@ addAllParens topLevelParen = \case
 remSuperfluousParens :: Int -> OpTree -> OpTree
 remSuperfluousParens outerFixity = \case
   x@OpLeaf{}                 -> x
+  OpUnknown _ locO locC c [] -> OpUnknown NoParen locO locC c []
   x@OpUnknown{}              -> x
   OpKnown paren locO locC fixity c cs ->
     OpKnown