Return empty ldcache if cache does not exist

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/ldcache/empty.go

@@ -0,0 +1,37 @@
+/**
+# Copyright (c) NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+**/
+
+package ldcache
+
+import "github.com/NVIDIA/nvidia-container-toolkit/internal/logger"
+
+type empty struct {
+	logger logger.Interface
+	path   string
+}
+
+var _ LDCache = (*empty)(nil)
+
+// List always returns nil for an empty ldcache
+func (e *empty) List() ([]string, []string) {
+	return nil, nil
+}
+
+// Lookup logs a debug message and returns nil for an empty ldcache
+func (e *empty) Lookup(prefixes ...string) ([]string, []string) {
+	e.logger.Debugf("Calling Lookup(%v) on empty ldcache: %v", prefixes, e.path)
+	return nil, nil
+}