[MJAVADOC-767] javadoc creates invalid --patch-module statements (#225)

Fixes empty --patch-module command line entries

When using an exclude filter, it is possible that the plugin creates
javadoc --patch-module command line options, that do not actually have
a value.

This changes skips such empty entries.

src/it/projects/MJAVADOC-767/doc/pom.xml

@@ -0,0 +1,69 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+~   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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.apache.maven.plugins.javadoc.it</groupId>
+        <artifactId>mjavadoc767</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>doc</artifactId>
+    <packaging>pom</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.maven.plugins.javadoc.it</groupId>
+            <artifactId>thing1</artifactId>
+            <version>1.0-SNAPSHOT</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven.plugins.javadoc.it</groupId>
+            <artifactId>thing2</artifactId>
+            <version>1.0-SNAPSHOT</version>
+        </dependency>
+   </dependencies>
+
+   <build>
+       <plugins>
+           <plugin>
+               <artifactId>maven-javadoc-plugin</artifactId>
+               <version>@project.version@</version>
+               <executions>
+                   <execution>
+                       <id>javadoc-jar</id>
+                       <goals>
+                           <goal>aggregate-jar</goal>
+                       </goals>
+                       <phase>package</phase>
+                       <configuration>
+                           <jvmVersion>9</jvmVersion>
+                           <skip>false</skip>
+                           <includeDependencySources>true</includeDependencySources>
+                           <detectOfflineLinks>false</detectOfflineLinks>
+                           <dependencySourceIncludes>
+                               <dependencySourceInclude>*:*</dependencySourceInclude>
+                           </dependencySourceIncludes>
+                           <dependencySourceExcludes>
+                               <dependencySourceExclude>*:thing2</dependencySourceExclude>
+                           </dependencySourceExcludes>
+                       </configuration>
+                   </execution>
+               </executions>
+           </plugin>
+       </plugins>
+   </build>
+</project>

src/it/projects/MJAVADOC-767/invoker.properties

@@ -0,0 +1,19 @@
+# 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.
+
+invoker.goals= package
+invoker.java.version = 9+

src/it/projects/MJAVADOC-767/pom.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+~   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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.apache.maven.plugins.javadoc.it</groupId>
+    <artifactId>mjavadoc767</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>pom</packaging>
+
+    <url>https://issues.apache.org/jira/browse/MJAVADOC-767</url>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>9</maven.compiler.source>
+        <maven.compiler.target>9</maven.compiler.target>
+    </properties>
+
+    <modules>
+        <module>thing1</module>
+        <module>thing2</module>
+        <module>doc</module>
+    </modules>
+</project>

src/it/projects/MJAVADOC-767/thing1/pom.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+~   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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.apache.maven.plugins.javadoc.it</groupId>
+        <artifactId>mjavadoc767</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>thing1</artifactId>
+    <packaging>jar</packaging>
+</project>

src/it/projects/MJAVADOC-767/thing1/src/main/java/jdbug/thing1/Main.java

@@ -0,0 +1,26 @@
+/*
+ * 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.
+ */
+
+package jdbug.thing1;
+
+public final class Main {
+    public static final void main(String ... args) throws Exception {
+        System.out.println("Hello, World!");
+    }
+}

src/it/projects/MJAVADOC-767/thing1/src/main/java/module-info.java

@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+module jdbug.thing1 {
+    exports jdbug.thing1;
+}

src/it/projects/MJAVADOC-767/thing2/pom.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+~   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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.apache.maven.plugins.javadoc.it</groupId>
+        <artifactId>mjavadoc767</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>thing2</artifactId>
+    <packaging>jar</packaging>
+</project>

src/it/projects/MJAVADOC-767/thing2/src/main/java/jdbug/thing2/Main.java

@@ -0,0 +1,26 @@
+/*
+ * 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.
+ */
+
+package jdbug.thing2;
+
+public final class Main {
+    public static final void main(String ... args) throws Exception {
+        System.out.println("Hello, World!");
+    }
+}

src/it/projects/MJAVADOC-767/thing2/src/main/java/module-info.java

@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+module jdbug.thing2 {
+    exports jdbug.thing2;
+}

src/main/java/org/apache/maven/plugins/javadoc/AbstractJavadocMojo.java

@@ -4594,12 +4594,14 @@ private void addJavadocOptions(
         }
 
         for (Entry<String, Collection<Path>> entry : patchModules.entrySet()) {
-            addArgIfNotEmpty(
-                    arguments,
-                    "--patch-module",
-                    entry.getKey() + '=' + JavadocUtil.quotedPathArgument(getSourcePath(entry.getValue())),
-                    false,
-                    false);
+            if (!entry.getValue().isEmpty()) {
+                addArgIfNotEmpty(
+                        arguments,
+                        "--patch-module",
+                        entry.getKey() + '=' + JavadocUtil.quotedPathArgument(getSourcePath(entry.getValue())),
+                        false,
+                        false);
+            }
         }
 
         if (doclet != null && !doclet.isEmpty()) {