Remove guard clause due to bad method invocation.

The no-arg `getFirstLevelModuleDependencies()` method is only availabe
on the default implementation and is not defined on the interface for
LenientConfiguration. The anonymous implementation returned from when
any empty dependency set is used lacks this helper method, resulting
in a runtime failure. The interface method is now invoked with a
filter to collect everything.

src/main/groovy/com/github/benmanes/gradle/versions/DependencyUpdates.groovy

@@ -20,6 +20,8 @@ import org.gradle.api.artifacts.Dependency
 import org.gradle.api.artifacts.ExternalDependency
 import org.gradle.api.internal.artifacts.version.LatestVersionSemanticComparator
 
+import static org.gradle.api.specs.Specs.SATISFIES_ALL
+
 /**
  * An evaluator for reporting of which dependencies have newer versions.
  * <p>
@@ -42,12 +44,12 @@ class DependencyUpdates {
     def current = getProjectAndBuildscriptDependencies()
     def (resolved, unresolved) = resolveLatestDepedencies(current)
     def (currentVersions, latestVersions, upToDateVersions, downgradeVersions, upgradeVersions) =
-      getVersionMapping(current, resolved)
+      composeVersionMapping(current, resolved)
     new DependencyUpdatesReporter(project, revision, currentVersions, latestVersions,
       upToDateVersions, downgradeVersions, upgradeVersions, unresolved)
   }
 
-  /** Returns {@link ExternalDependency} collected from the project and buildscript. */
+  /** Returns {@link ExternalDependency} collected from all projects and buildscripts. */
   private def getProjectAndBuildscriptDependencies() {
     project.allprojects.collectMany{ proj ->
       def configurations = (proj.configurations + proj.buildscript.configurations)
@@ -60,19 +62,16 @@ class DependencyUpdates {
    * the latest dependencies to determine the newest versions.
    */
   private def resolveLatestDepedencies(current) {
-    if (current.empty) {
-      return [[], []]
-    }
-    def unresolved = current.collect { dependency ->
+    def latest = current.collect { dependency ->
       project.dependencies.create(group: dependency.group, name: dependency.name,
           version: "latest.${revision}") {
         transitive = false
       }
     }
     resolveWithAllRepositories {
-      def lenient = project.configurations.detachedConfiguration(unresolved as Dependency[])
+      def conf = project.configurations.detachedConfiguration(latest as Dependency[])
         .resolvedConfiguration.lenientConfiguration
-      [lenient.firstLevelModuleDependencies, lenient.unresolvedModuleDependencies]
+      [conf.getFirstLevelModuleDependencies(SATISFIES_ALL), conf.unresolvedModuleDependencies]
     }
   }
 
@@ -100,7 +99,7 @@ class DependencyUpdates {
   }
 
   /** Organizes the dependencies into version mappings. */
-  private def getVersionMapping(current, resolved) {
+  private def composeVersionMapping(current, resolved) {
     def currentVersions = current.collectEntries { dependency ->
        [keyOf(dependency), dependency.version]
     }

src/test/groovy/com/github/benmanes/gradle/versions/DependencyUpdatesSpec.groovy

@@ -120,7 +120,7 @@ class DependencyUpdatesSpec extends Specification {
     given:
       def (rootProject, childProject, leafProject) = multiProject()
       addRepositoryTo(childProject)
-      addDependenciesTo(leafProject)
+      addDependenciesTo(rootProject)
     when:
       def reporter = evaluate(rootProject, revision)
       reporter.writeToConsole()