read empty list of frozen violations correctly #457

By default `Splitter.on(..).splitToList("")` returns a list containing one element (the empty string). This leads to an inconsistent behavior, because saving no lines will in turn return one line on read. Configuring `Splitter` via `omitEmptyStrings()` we can fix this behavior by skipping all empty lines, which makes sense in general.

Resolves: #456

Signed-off-by: Manfred Hanke <Manfred.Hanke@tngtech.com>

archunit/src/main/java/com/tngtech/archunit/library/freeze/ViolationStoreFactory.java

@@ -183,7 +183,7 @@ public List<String> getViolations(ArchRule rule) {
 
         private List<String> readLines(String ruleDetailsFileName) {
             String violationsText = readStoreFile(ruleDetailsFileName);
-            List<String> lines = Splitter.on(UNESCAPED_LINE_BREAK_PATTERN).splitToList(violationsText);
+            List<String> lines = Splitter.on(UNESCAPED_LINE_BREAK_PATTERN).omitEmptyStrings().splitToList(violationsText);
             return unescape(lines);
         }
 

archunit/src/test/java/com/tngtech/archunit/library/freeze/TextFileBasedViolationStoreTest.java

@@ -79,6 +79,15 @@ public void reads_violations_of_single_rule_from_configured_folder() {
         assertThat(storedViolations).containsOnly("first violation", "second violation");
     }
 
+    @Test
+    public void reads_empty_list_of_violations() {
+        store.save(defaultRule(), ImmutableList.<String>of());
+
+        List<String> storedViolations = store.getViolations(defaultRule());
+
+        assertThat(storedViolations).isEmpty();
+    }
+
     @Test
     public void stores_violations_of_multiple_rules() {
         ArchRule firstRule = rule("first rule");