Tolerate exclusions declared without a groupId or artifactId

Fixes gh-293

Author: wilkinsona

src/main/java/io/spring/gradle/dependencymanagement/internal/Exclusion.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2020 the original author or authors.
+ * Copyright 2014-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,8 +34,8 @@ public class Exclusion {
      * @param artifactId artifact ID
      */
     public Exclusion(String groupId, String artifactId) {
-        this.groupId = groupId;
-        this.artifactId = artifactId;
+        this.groupId = (groupId != null) ? groupId : "";
+        this.artifactId = (artifactId != null) ? artifactId : "";
     }
 
     /**

src/test/groovy/io/spring/gradle/dependencymanagement/DependencyManagementPluginSpec.groovy

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2020 the original author or authors.
+ * Copyright 2014-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -1472,4 +1472,23 @@ public class DependencyManagementPluginSpec extends Specification {
         project.dependencyManagement.managedVersions.isEmpty()
     }
 
+    def 'An exclusion that is malformed is tolerated'() {
+        given: 'A project with the plugin applied'
+        project.apply plugin: 'io.spring.dependency-management'
+        project.apply plugin: 'java'
+        project.repositories {
+            maven { url new File("src/test/resources/maven-repo").toURI().toURL().toString() }
+        }
+        when: 'it depends on a module with malformed exclusions'
+        project.dependencies {
+            compile 'test:malformed-exclude:1.0'
+        }
+        def files = project.configurations.compile.resolve()
+        then: "the project can be built"
+        files.size() == 3
+        files.collect { it.name }.containsAll(['malformed-exclude-1.0.jar',
+                                               'spring-core-4.1.2.RELEASE.jar',
+                                               'commons-logging-1.1.3.jar'])
+    }
+
 }

src/test/resources/maven-repo/test/malformed-exclude/1.0/malformed-exclude-1.0.jar

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>test</groupId>
+    <artifactId>malformed-exclude</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-core</artifactId>
+            <version>4.1.2.RELEASE</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+    </dependencies>
+
+</project>