fix output var may be nullptr and cause segment fault bug (#40079)

paddle/fluid/framework/operator.cc

@@ -2106,6 +2106,8 @@ void OperatorWithKernel::BuildPhiKernelContext(
     for (size_t offset = 0; offset < outs_vector.size(); ++offset) {
       phi::TensorBase* tensor_out = nullptr;
       auto* var = outs_vector[offset];
+
+      if (var) {
         if (var->template IsType<framework::LoDTensor>()) {
           tensor_out = var->template GetMutable<framework::LoDTensor>();
         } else if (var->template IsType<phi::SelectedRows>()) {
@@ -2115,6 +2117,8 @@ void OperatorWithKernel::BuildPhiKernelContext(
               "Unsupported output `%s` type when call pt kernel.",
               framework::ToTypeName(var->Type())));
         }
+      }
+
       pt_kernel_context->EmplaceBackOutputWithoutSetRange(tensor_out);
     }
 

paddle/fluid/imperative/prepared_operator.h

@@ -314,6 +314,7 @@ void BuildDygraphPhiKernelContext(
 
       phi::TensorBase* tensor_out = nullptr;
       auto* var = outs_vector[offset]->MutableVar();
+      if (var) {
         if (var->template IsType<phi::DenseTensor>()) {
           tensor_out = var->template GetMutable<phi::DenseTensor>();
         } else if (var->template IsType<phi::SelectedRows>()) {
@@ -323,6 +324,8 @@ void BuildDygraphPhiKernelContext(
               "Unsupported output `%s` type when call pt kernel.",
               framework::ToTypeName(var->Type())));
         }
+      }
+
       kernel_ctx->EmplaceBackOutputWithoutSetRange(tensor_out);
     }
     kernel_ctx->AssignOutputRange(std::make_pair(start_idx, end_idx), i);