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

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

Index: pkg/analyzer/lib/src/task/strong_mode.dart
diff --git a/pkg/analyzer/lib/src/task/strong_mode.dart b/pkg/analyzer/lib/src/task/strong_mode.dart
index 0ab8a8bbff15dd5850f1a372a2a74ef9f3050c92..3d621cf0043670395b1f96baf494069035793162 100644
--- a/pkg/analyzer/lib/src/task/strong_mode.dart
+++ b/pkg/analyzer/lib/src/task/strong_mode.dart
@@ -29,7 +29,10 @@ void setFieldType(VariableElement field, DartType 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;
+      }
     }
   }
 }