Enable EqualsAvoidNull in checkstyle

airsonic-main/src/main/java/org/airsonic/player/service/MediaFileService.java

@@ -459,7 +459,7 @@ public class MediaFileService {
         }
 
         // Exclude all hidden files starting with a single "." or "@eaDir" (thumbnail dir created on Synology devices).
-        return (name.startsWith(".") && !name.startsWith("..")) || name.startsWith("@eaDir") || name.equals("Thumbs.db");
+        return (name.startsWith(".") && !name.startsWith("..")) || name.startsWith("@eaDir") || "Thumbs.db".equals(name);
     }
 
     private MediaFile createMediaFile(File file) {

airsonic-main/src/main/java/org/airsonic/player/service/metadata/JaudiotaggerParser.java

@@ -360,17 +360,17 @@ public class JaudiotaggerParser extends MetaDataParser {
 
         String format = FilenameUtils.getExtension(file.getName()).toLowerCase();
 
-        return format.equals("mp3") ||
+        return "mp3".equals(format) ||
-                format.equals("m4a") ||
+               "m4a".equals(format) ||
-                format.equals("m4b") ||
+               "m4b".equals(format) ||
-                format.equals("aac") ||
+               "aac".equals(format) ||
-                format.equals("ogg") ||
+               "ogg".equals(format) ||
-                format.equals("flac") ||
+               "flac".equals(format) ||
-                format.equals("wav") ||
+               "wav".equals(format) ||
-                format.equals("mpc") ||
+               "mpc".equals(format) ||
-                format.equals("mp+") ||
+               "mp+".equals(format) ||
-                format.equals("ape") ||
+               "ape".equals(format) ||
-                format.equals("wma");
+               "wma".equals(format);
     }
 
     /**
@@ -393,4 +393,4 @@ public class JaudiotaggerParser extends MetaDataParser {
         Tag tag = audioFile.getTag();
         return tag == null ? null : tag.getFirstArtwork();
     }
-}
+}

airsonic-main/src/main/java/org/airsonic/player/theme/CustomThemeSource.java

@@ -42,7 +42,7 @@ public class CustomThemeSource extends ResourceBundleThemeSource {
 
         // Create parent theme recursively.
         for (Theme theme : settingsService.getAvailableThemes()) {
-            if (basename.equals(basenamePrefix + theme.getId()) && theme.getParent() != null) {
+            if ((basenamePrefix + theme.getId()).equals(basename) && theme.getParent() != null) {
                 String parent = basenamePrefix + theme.getParent();
                 messageSource.setParentMessageSource(createMessageSource(parent));
                 break;

checkstyle.xml

@@ -22,6 +22,7 @@
         </module>
         <module name="DefaultComesLast"/>
         <module name="EmptyStatement"/>
+        <module name="EqualsAvoidNull"/>
         <module name="EqualsHashCode"/>
         <module name="InnerAssignment"/>
         <module name="RedundantImport"/>