fix NPE in PropertyPlaceHolder

settings-api/src/main/java/org/xbib/settings/PropertyPlaceholder.java

@@ -46,6 +46,9 @@ public class PropertyPlaceholder {
     protected String parseStringValue(String value,
                                       PlaceholderResolver placeholderResolver,
                                       Set<String> visitedPlaceholders) {
+        if (value == null) {
+            return null;
+        }
         StringBuilder sb = new StringBuilder(value);
         int startIndex = value.indexOf(this.placeholderPrefix);
         while (startIndex != -1) {
@@ -53,8 +56,7 @@ public class PropertyPlaceholder {
             if (endIndex != -1) {
                 String placeholder = sb.substring(startIndex + this.placeholderPrefix.length(), endIndex);
                 if (!visitedPlaceholders.add(placeholder)) {
-                    throw new IllegalArgumentException(
+                    throw new IllegalArgumentException("Circular placeholder reference '" + placeholder + "' in property definitions");
-                            "Circular placeholder reference '" + placeholder + "' in property definitions");
                 }
                 placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
                 int defaultValueIdx = placeholder.indexOf(':');

settings-content/src/test/java/org/xbib/settings/content/test/SettingsTest.java

@@ -23,6 +23,7 @@ import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
@@ -116,6 +117,15 @@ public class SettingsTest {
         assertEquals(LocalDate.now().getYear(), Integer.parseInt(settings.get("date")));
     }
 
+    @Test
+    public void testPropertyReplaceNull() {
+        Settings settings = Settings.settingsBuilder()
+                .put("null", null)
+                .replacePropertyPlaceholders()
+                .build();
+        assertNull(settings.get("null"));
+    }
+
     @Test
     public void testSystemEnvironment() {
         Settings settings = Settings.settingsBuilder()

settings-datastructures/src/test/java/org/xbib/settings/datastructures/test/SettingsTest.java

@@ -13,6 +13,7 @@ import java.util.Map;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class SettingsTest {
@@ -89,6 +90,15 @@ public class SettingsTest {
         assertEquals(LocalDate.now().getYear(), Integer.parseInt(settings.get("date")));
     }
 
+    @Test
+    public void testPropertyReplaceNull() {
+        Settings settings = Settings.settingsBuilder()
+                .put("null", null)
+                .replacePropertyPlaceholders()
+                .build();
+        assertNull(settings.get("null"));
+    }
+
     @Test
     public void testSystemEnvironment() {
         Settings settings = Settings.settingsBuilder()