Fix for instance fields inference when a setter has no parameter.

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 9208b991d3f082168a6397ad4d265a1ed727379c..e803d2df487c4b6dcb65b3e944076c980100d294 100644
--- a/pkg/analyzer/lib/src/task/strong_mode.dart
+++ b/pkg/analyzer/lib/src/task/strong_mode.dart
@@ -273,11 +273,14 @@ class InstanceMemberInferrer {
     if (element.kind == ElementKind.GETTER) {
       (element as ExecutableElementImpl).returnType = typeResult.type;
     } else if (element.kind == ElementKind.SETTER) {
-      var parameter = element.parameters[0] as ParameterElementImpl;
-      if (parameter.hasImplicitType) {
-        parameter.type = typeResult.type;
+      List<ParameterElement> parameters = element.parameters;
+      if (parameters.isNotEmpty) {
+        var parameter = parameters[0] as ParameterElementImpl;
+        if (parameter.hasImplicitType) {
+          parameter.type = typeResult.type;
+        }
+        parameter.inheritsCovariant = typeResult.isCovariant;
       }
-      parameter.inheritsCovariant = typeResult.isCovariant;
     }
     setFieldType(element.variable, typeResult.type);
   }