Issue 26147. Don't attempt to set the type of the parameter for setters without parameters.

pkg/analyzer/lib/src/task/strong_mode.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.task.strong_mode;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
@@ skipping 11 matching lines @@
  * synthetic getter/setter types.
  */
 void setFieldType(VariableElement field, DartType newType) {
   (field as VariableElementImpl).type = newType;
   if (field.initializer != null) {
     (field.initializer as ExecutableElementImpl).returnType = newType;
   }
   if (field is PropertyInducingElementImpl) {
     (field.getter as ExecutableElementImpl).returnType = newType;
     if (!field.isFinal && !field.isConst) {
-      (field.setter.parameters[0] as ParameterElementImpl).type = newType;
+      List<ParameterElement> setterParameters = field.setter.parameters;
+      if (setterParameters.isNotEmpty) {
+        (setterParameters[0] as ParameterElementImpl).type = newType;
+      }
     }
   }
 }
 
 /**
  * Return the element for the single parameter of the given [setter], or `null`
  * if the executable element is not a setter or does not have a single
  * parameter.
  */
 ParameterElement _getParameter(ExecutableElement setter) {
@@ skipping 430 matching lines @@
         results.add(element);
       }
     }
   }
 }
 
 /**
  * A class of exception that is not used anywhere else.
  */
 class _CycleException implements Exception {}