Don't rely on the existence of an element in field gets.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
diff --git a/lib/compiler/implementation/ssa/optimize.dart b/lib/compiler/implementation/ssa/optimize.dart
index ef7273adb755e001b8be7f22cdfdd358386d5dac..e84c0e907ebf24ccdc52c1f2bb6dbe09596fc028 100644
--- a/lib/compiler/implementation/ssa/optimize.dart
+++ b/lib/compiler/implementation/ssa/optimize.dart
@@ -1209,13 +1209,15 @@ class BaseRecompilationVisitor extends HBaseVisitor {
   void visitFieldGet(HFieldGet node) {
     if (!node.element.isInstanceMember()) return;
     Element field = node.element;
-    HType type = backend.optimisticFieldTypeAfterConstruction(field);
-    if (!type.isUnknown()) {
-      // Allow handling even if we haven't seen any types for this
-      // field yet. There might still be only one setter in an
-      // initializer list or constructor body and recompilation
-      // can therefore pay off.
-      handleFieldGet(node, type);
+    if (field != null) {
+      HType type = backend.optimisticFieldTypeAfterConstruction(field);
+      if (!type.isUnknown()) {
+        // Allow handling even if we haven't seen any types for this
+        // field yet. There might still be only one setter in an
+        // initializer list or constructor body and recompilation
+        // can therefore pay off.
+        handleFieldGet(node, type);
+      }
     }
   }