Guard against missing element (issue 26685)

pkg/analysis_server/lib/src/services/completion/dart/optype.dart

Index: pkg/analysis_server/lib/src/services/completion/dart/optype.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/optype.dart b/pkg/analysis_server/lib/src/services/completion/dart/optype.dart
index 995ec2756827c7dd8c11bf8d13dc315097fb652a..917542cdfb92623bc8264982406a531c26e18fa1 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/optype.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/optype.dart
@@ -556,7 +556,7 @@ class _OpTypeAstVisitor extends GeneralizingAstVisitor {
         if (node.parent is VariableDeclaration) {
           VariableDeclaration varDeclaration =
               node.parent as VariableDeclaration;
-          localTypeAssertion = varDeclaration.element.type;
+          localTypeAssertion = varDeclaration.element?.type;
         } else if (node.parent is AssignmentExpression) {
           AssignmentExpression assignmentExpression =
               node.parent as AssignmentExpression;