Fail fast when a managed dependency is configured with no artifactId

Closes gh-231

Author: wilkinsona

src/main/java/io/spring/gradle/dependencymanagement/internal/dsl/StandardDependenciesHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2017 the original author or authors.
+ * Copyright 2014-2019 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.
@@ -74,7 +74,8 @@ public void dependency(String id, Closure closure) {
     @Override
     public void dependency(String id, Action<DependencyHandler> action) {
         String[] components = id.split(":");
-        if (components.length != 3) {
+        if (components.length != 3 || components[0].length() == 0 ||
+                components[1].length() == 0 || components[2].length() == 0) {
             throw new InvalidUserDataException("Dependency identifier '" + id + "' is malformed. The required form is"
                     + " 'group:name:version'");
         }

src/test/groovy/io/spring/gradle/dependencymanagement/internal/dsl/StandardDependenciesHandlerSpec.groovy

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2018 the original author or authors.
+ * Copyright 2014-2019 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.
@@ -46,6 +46,15 @@ class StandardDependenciesHandlerSpec extends Specification {
         1 * container.addManagedVersion(configuration, "group", "name", "1.0", _)
     }
 
+    def 'Dependency configured with an empty artifactId is rejected'() {
+        when: 'A dependency is configured with not artifactId'
+        handler.dependency 'com.example::1.0'
+
+        then: 'An exception with an appropriate message is thrown'
+        def ex = thrown(GradleException)
+        ex.message == "Dependency identifier 'com.example::1.0' is malformed. The required form is 'group:name:version'"
+    }
+
     def 'Dependency set can be configured using a Map with GString values'() {
         when:
         def group = "group"