diff --git a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java
index f14e09a..d5c7a95 100644
--- a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java
+++ b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfiguration.java
@@ -48,16 +48,11 @@ public class BuilderConfiguration {
     @Bean
     public Map<RuleSource, List<String>> checkClasses(final PackageScanner packageScanner) {
         return Stream.of(RuleSource.values())
-                .map(source -> entry(source, packageScanner.apply(source)
-                        .collect(Collectors.toList())))
+                .map(source -> entry(source, packageScanner.apply(source)))
                 .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
     }
 
-    private static AbstractMap.SimpleEntry<RuleSource, List<String>> entry(
-            final RuleSource key,
-            final List<String> value
-                                                                          ) {
+    private static <K, V> AbstractMap.SimpleEntry<K, V> entry(final K key, final V value) {
         return new AbstractMap.SimpleEntry<>(key, value);
     }
-
 }
diff --git a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java
index 0628f4d..f193f1b 100644
--- a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java
+++ b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScanner.java
@@ -24,7 +24,8 @@ package net.kemitix.checkstyle.ruleset.builder;
 import io.github.lukehutch.fastclasspathscanner.FastClasspathScanner;
 import org.springframework.stereotype.Service;
 
-import java.util.stream.Stream;
+import java.util.List;
+import java.util.stream.Collectors;
 
 /**
  * Default implementation of {@link PackageScanner}.
@@ -35,12 +36,13 @@ import java.util.stream.Stream;
 public class DefaultPackageScanner implements PackageScanner {
 
     @Override
-    public final Stream<String> apply(final RuleSource ruleSource) {
+    public final List<String> apply(final RuleSource ruleSource) {
         final String basePackage = ruleSource.getBasePackage();
         return new FastClasspathScanner(basePackage)
                 .scan()
                 .getNamesOfAllStandardClasses()
                 .stream()
-                .filter(packageName -> packageName.startsWith(basePackage));
+                .filter(packageName -> packageName.startsWith(basePackage))
+                .collect(Collectors.toList());
     }
 }
diff --git a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java
index 7cc8c2b..02a59df 100644
--- a/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java
+++ b/builder/src/main/java/net/kemitix/checkstyle/ruleset/builder/PackageScanner.java
@@ -21,14 +21,14 @@
 
 package net.kemitix.checkstyle.ruleset.builder;
 
+import java.util.List;
 import java.util.function.Function;
-import java.util.stream.Stream;
 
 /**
  * Scans a package for all classes.
  *
  * @author Paul Campbell (pcampbell@kemitix.net).
  */
-interface PackageScanner extends Function<RuleSource, Stream<String>> {
+interface PackageScanner extends Function<RuleSource, List<String>> {
 
 }
diff --git a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java
index 63eb6c2..f9afaa8 100644
--- a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java
+++ b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/BuilderConfigurationTest.java
@@ -9,6 +9,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.stream.Stream;
 
+import static java.util.Collections.singletonList;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
@@ -20,29 +21,20 @@ import static org.mockito.Mockito.mock;
  */
 public class BuilderConfigurationTest {
 
-    @Test
-    public void canGetClassPath() throws IOException {
-        //when
-        final BuilderConfiguration builderConfiguration = new BuilderConfiguration();
-        final ClassPath classPath = builderConfiguration.classPath(builderConfiguration.getClass().getClassLoader());
-        //then
-        assertThat(classPath).isNotNull();
-    }
-
     @Test
     public void canGetCheckClasses() {
         //given
         final PackageScanner packageScanner = mock(PackageScanner.class);
         final String checkstyleClass = "checkstyle class";
-        given(packageScanner.apply(RuleSource.CHECKSTYLE)).willReturn(Stream.of(checkstyleClass));
+        given(packageScanner.apply(RuleSource.CHECKSTYLE)).willReturn(singletonList(checkstyleClass));
         final String sevntuClass = "sevntu class";
-        given(packageScanner.apply(RuleSource.SEVNTU)).willReturn(Stream.of(sevntuClass));
+        given(packageScanner.apply(RuleSource.SEVNTU)).willReturn(singletonList(sevntuClass));
         //when
         final Map<RuleSource, List<String>> checkClasses = new BuilderConfiguration().checkClasses(packageScanner);
         //then
         assertThat(checkClasses).containsOnlyKeys(RuleSource.values());
         assertThat(checkClasses)
-                .containsEntry(RuleSource.CHECKSTYLE, Collections.singletonList(checkstyleClass))
-                .containsEntry(RuleSource.SEVNTU, Collections.singletonList(sevntuClass));
+                .containsEntry(RuleSource.CHECKSTYLE, singletonList(checkstyleClass))
+                .containsEntry(RuleSource.SEVNTU, singletonList(sevntuClass));
     }
 }
diff --git a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java
index 92ca00b..7b5a02e 100644
--- a/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java
+++ b/builder/src/test/java/net/kemitix/checkstyle/ruleset/builder/DefaultPackageScannerTest.java
@@ -2,6 +2,7 @@ package net.kemitix.checkstyle.ruleset.builder;
 
 import org.junit.Test;
 
+import java.util.List;
 import java.util.stream.Stream;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -18,7 +19,7 @@ public class DefaultPackageScannerTest {
     @Test
     public void canScanCheckstylePackage() {
         //when
-        final Stream<String> result = scanner.apply(RuleSource.CHECKSTYLE);
+        final List<String> result = scanner.apply(RuleSource.CHECKSTYLE);
         //then
         assertThat(result).allMatch(cn -> cn.startsWith(RuleSource.CHECKSTYLE.getBasePackage()))
                           .contains("com.puppycrawl.tools.checkstyle.checks.sizes.FileLengthCheck");
@@ -27,7 +28,7 @@ public class DefaultPackageScannerTest {
     @Test
     public void canScanSevntuPackage() {
         //when
-        final Stream<String> result = scanner.apply(RuleSource.SEVNTU);
+        final List<String> result = scanner.apply(RuleSource.SEVNTU);
         //then
         assertThat(result).allMatch(cn -> cn.startsWith(RuleSource.SEVNTU.getBasePackage()))
                           .contains("com.github.sevntu.checkstyle.checks.design.NestedSwitchCheck");