Guard against parameters with no types (issue 25692)

pkg/analyzer/lib/src/dart/element/type.dart

Index: pkg/analyzer/lib/src/dart/element/type.dart
diff --git a/pkg/analyzer/lib/src/dart/element/type.dart b/pkg/analyzer/lib/src/dart/element/type.dart
index 2d03cccbafe9901d83201db4f6bb52e5ba5b902b..aedd7b2ac723a2194ab07f30b3eece2a8ff05fdf 100644
--- a/pkg/analyzer/lib/src/dart/element/type.dart
+++ b/pkg/analyzer/lib/src/dart/element/type.dart
@@ -739,7 +739,7 @@ class FunctionTypeImpl extends TypeImpl implements FunctionType {
         TypeParameterTypeImpl.getTypes(this.typeParameters);
     for (ParameterElement parameter in baseParameters) {
       if (parameter.parameterKind == kind) {
-        TypeImpl type = parameter.type;
+        TypeImpl type = parameter.type ?? DynamicTypeImpl.instance;
         if (typeArguments.length != 0 &&
             typeArguments.length == typeParameters.length) {
           type = type.substitute2(typeArguments, typeParameters, newPrune);