Abstract nullary toString does not have a parameter list in 2.12.8

[Win Wang]

trait T {
    def toString: String
}
trait T2 {
    override def toString: String
}
trait T3 {
    override def toString: String = ""
}
trait T4 {
    def toString(): String
}
trait T5 {
    override def toString(): String
}
trait T6 {
    override def toString(): String = ""
}
abstract class A {
    def toString: String
}
abstract class A2 {
    override def toString: String
}
abstract class A3 {
    override def toString: String = ""
}
abstract class A4 {
    def toString(): String
}
abstract class A5 {
    override def toString(): String
}
abstract class A6 {
    override def toString(): String = ""
}
class C extends T {
    override def toString: String = ""
}
class C2 extends T2 {
    override def toString: String = ""
}
class C3 extends T3 {
    override def toString: String = ""
}
class D extends T {
    override def toString(): String = ""
}
class E {
    override def toString: String = ""
}
class F extends A {
    override def toString: String = ""
}

different nsc (-) vs rsc (+): T.scala: _empty_/A#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
different nsc (-) vs rsc (+): T.scala: _empty_/A2#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
different nsc (-) vs rsc (+): T.scala: _empty_/C#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
different nsc (-) vs rsc (+): T.scala: _empty_/C2#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
different nsc (-) vs rsc (+): T.scala: _empty_/F#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
different nsc (-) vs rsc (+): T.scala: _empty_/T#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
different nsc (-) vs rsc (+): T.scala: _empty_/T2#toString().
 language: SCALA
 signature {
   method_signature {
     type_parameters {
     }
+    parameter_lists {
+    }
     return_type {
       type_ref {
         prefix {
         }
         symbol: "scala/Predef.String#"
7 problems found