[MENFORCER-395] Fix NPE in requireReleaseDeps 

diff --git a/enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/RequireReleaseDeps.java b/enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/RequireReleaseDeps.java
index 208f8ac..783ea70 100644
--- a/enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/RequireReleaseDeps.java
+++ b/enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/RequireReleaseDeps.java
@@ -141,15 +141,17 @@
         Set<Artifact> foundSnapshots = new HashSet<>();
 
         Set<Artifact> filteredDependencies = filterArtifacts( dependencies );
-        
-        for ( Artifact artifact : filteredDependencies )
+
+        if ( filteredDependencies != null )
         {
-            if ( artifact.isSnapshot() )
+            for ( Artifact artifact : filteredDependencies )
             {
-                foundSnapshots.add( artifact );
+                if ( artifact.isSnapshot() )
+                {
+                    foundSnapshots.add( artifact );
+                }
             }
         }
-
         return foundSnapshots;
     }
     
diff --git a/maven-enforcer-plugin/src/it/projects/MENFORCER-395/pom.xml b/maven-enforcer-plugin/src/it/projects/MENFORCER-395/pom.xml
new file mode 100644
index 0000000..54edc98
--- /dev/null
+++ b/maven-enforcer-plugin/src/it/projects/MENFORCER-395/pom.xml
@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you 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.
+-->
+
+<project>
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.apache.maven.its.enforcer</groupId>
+  <artifactId>minimal-test</artifactId>
+  <version>0.0.1</version>
+  <packaging>jar</packaging>
+  <description>Minimal test for NPE in maven-enforcer-plugin:3.0.0</description>
+  <properties>
+    <java.source>1.8</java.source>
+    <java.target>1.8</java.target>
+  </properties>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-enforcer-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <id>enforce-no-snapshots</id>
+            <goals>
+              <goal>enforce</goal>
+            </goals>
+            <configuration>
+              <rules>
+                <requireReleaseDeps>
+                  <includes>
+                    <include>testgroup:testartifact</include>
+                  </includes>
+                </requireReleaseDeps>
+              </rules>
+              <fail>true</fail>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>
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