Merge branch '__rultor'

qulice-pmd/src/main/resources/com/qulice/pmd/ruleset.xml

@@ -198,4 +198,23 @@ OF THE POSSIBILITY OF SUCH DAMAGE.
       </property>
     </properties>
   </rule>
+  <rule name="ReturnEmptyCollectionRatherThanNull" language="java" class="net.sourceforge.pmd.lang.rule.XPathRule" message="Returned null collection was found (NullCollection).">
+    <description>
+            Any method that returns an collection (i.e. an array or a List), it is better to return
+            an empty one rather than a null reference.
+        </description>
+    <priority>1</priority>
+    <properties>
+      <property name="version" value="2.0"/>
+      <!--Solve priority confict-->
+      <property name="xpath">
+        <value><![CDATA[
+                        //MethodDeclaration[
+                        (./ResultType/Type[pmd-java:typeIs('java.util.Collection') 
+                          or pmd-java:typeIs('java.util.Map') or @ArrayType=true()]) and
+                        (./Block/BlockStatement/Statement/ReturnStatement/Expression/PrimaryExpression/PrimaryPrefix/Literal/NullLiteral)
+                        ]]]></value>
+      </property>
+    </properties>
+  </rule>
 </ruleset>

qulice-pmd/src/test/java/com/qulice/pmd/EmptyCollectionRuleTest.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2011-2022 Qulice.com
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met: 1) Redistributions of source code must retain the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer. 2) Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials provided
+ * with the distribution. 3) Neither the name of the Qulice.com nor
+ * the names of its contributors may be used to endorse or promote
+ * products derived from this software without specific prior written
+ * permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
+ * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.qulice.pmd;
+
+import org.hamcrest.Matchers;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test case for ReturnEmptyCollectionRatherThanNull.
+ *
+ * @since 0.19
+ */
+public class EmptyCollectionRuleTest {
+    /**
+     * Makes sure that empty collections not returned as null.
+     * @throws Exception when something goes wrong
+     */
+    @Test
+    public void failsForNullCollection() throws Exception {
+        new PmdAssert(
+            "NullCollection.java",
+            Matchers.is(false),
+            Matchers.containsString(
+                "Returned null collection was found (NullCollection)."
+            )
+        ).validate();
+    }
+}

qulice-pmd/src/test/resources/com/qulice/pmd/NullCollection.java

@@ -0,0 +1,10 @@
+package emp;
+
+import java.util.List;
+
+class NullCollection {
+
+    public final List<Object> method() {
+        return null;
+    }
+}