Fix NPE in case the resource is AutoClosable and can be null (#287)

* Fix exception for resources that can be null

* Update version

* Add test for null auto-closable resource

gradle.properties

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-release_version=5.7.2
+release_version=5.7.3
 description='th2 common library (Java)'
 vcs_url=https://github.com/th2-net/th2-common-j
 kapt.include.compile.classpath=false

src/main/kotlin/com/exactpro/th2/common/schema/factory/LazyProvider.kt

@@ -20,7 +20,11 @@ import com.exactpro.th2.common.schema.factory.LazyProvider.ThrowableConsumer
 import java.util.concurrent.Callable
 import java.util.concurrent.atomic.AtomicReference
 
-internal class LazyProvider<T : Any?> private constructor(
+/**
+ * This is class is for internal use only. Please, keep that in mind when using it in another module
+ */
+// Kotlin internal keyword does not help here because you can still access the class from Java
+class LazyProvider<T : Any?> private constructor(
     private val name: String,
     private val supplier: Callable<out T>,
     private val onClose: ThrowableConsumer<in T>
@@ -48,7 +52,9 @@ internal class LazyProvider<T : Any?> private constructor(
         return if (reference.compareAndSet(null, State.Init)) {
             val holder = State.Hold(initialize())
             if (!reference.compareAndSet(State.Init, holder)) {
-                onClose.consume(holder.value)
+                if (holder.value != null) {
+                    onClose.consume(holder.value)
+                }
                 error("provider '$name' already closed")
             }
             holder
@@ -70,7 +76,7 @@ internal class LazyProvider<T : Any?> private constructor(
         }
 
         val prevState = reference.getAndSet(State.Closed)
-        if (prevState is State.Hold) {
+        if (prevState is State.Hold && prevState.value != null) {
             onClose.consume(prevState.value)
         }
     }

src/test/java/com/exactpro/th2/common/schema/factory/LazyProviderJavaTest.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2024 Exactpro (Exactpro Systems Limited)
+ *
+ * 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 com.exactpro.th2.common.schema.factory;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class LazyProviderJavaTest {
+    @Test
+    void nullAutoClosable() {
+        LazyProvider<AutoCloseable> provider = LazyProvider.lazyAutocloseable("test", () -> null);
+        var resource = provider.get();
+        Assertions.assertNull(resource, "unexpected resource value");
+        Assertions.assertDoesNotThrow(provider::close, "unexpected error when closing resource");
+    }
+}