Fix DM_DEFAULT_ENCODING SpotBugs violations (#6050)

core/src/main/java/hudson/FilePath.java

@@ -86,6 +86,7 @@ import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
 import java.net.URLConnection;
+import java.nio.charset.Charset;
 import java.nio.file.FileSystemException;
 import java.nio.file.FileSystems;
 import java.nio.file.Files;
@@ -2279,7 +2280,7 @@ public final class FilePath implements SerializableOnlyOverRemoting {
         private static final long serialVersionUID = 1L;       
         @Override
         public String invoke(File f, VirtualChannel channel) throws IOException, InterruptedException {
-            return new String(Files.readAllBytes(fileToPath(f)));
+            return new String(Files.readAllBytes(fileToPath(f)), Charset.defaultCharset());
         }
     }
 
@@ -2336,7 +2337,7 @@ public final class FilePath implements SerializableOnlyOverRemoting {
         public Void invoke(File f, VirtualChannel channel) throws IOException {
             mkdirs(f.getParentFile());
             try (OutputStream fos = Files.newOutputStream(fileToPath(f));
-                    Writer w = encoding != null ? new OutputStreamWriter(fos, encoding) : new OutputStreamWriter(fos)) {
+                    Writer w = encoding != null ? new OutputStreamWriter(fos, encoding) : new OutputStreamWriter(fos, Charset.defaultCharset())) {
                 w.write(content);
             }
             return null;
@@ -3611,5 +3612,4 @@ public final class FilePath implements SerializableOnlyOverRemoting {
         }
         private static final long serialVersionUID = 1L;
     }
-
 }