Console: Fix NPE on /configsidebar (ticket #2220)

Don't throw NPE translating null
Add note about split()
Fix form inside table

core/java/src/net/i2p/data/DataHelper.java

@@ -1950,6 +1950,9 @@ public class DataHelper {
      *  Same as s.split(regex) but caches the compiled pattern for speed.
      *  This saves about 10 microseconds (Bulldozer) on subsequent invocations.
      *
+     *  Note: For an input "" this returns [""], not a zero-length array.
+     *  This is the same behavior as String.split().
+     *
      *  @param s non-null
      *  @param regex non-null, don't forget to enclose multiple choices with []
      *  @throws java.util.regex.PatternSyntaxException unchecked
@@ -1965,6 +1968,9 @@ public class DataHelper {
      *  Same as s.split(regex, limit) but caches the compiled pattern for speed.
      *  This saves about 10 microseconds (Bulldozer) on subsequent invocations.
      *
+     *  Note: For an input "" this returns [""], not a zero-length array.
+     *  This is the same behavior as String.split().
+     *
      *  @param s non-null
      *  @param regex non-null, don't forget to enclose multiple choices with []
      *  @param limit result threshold

core/java/src/net/i2p/util/Translate.java

@@ -43,6 +43,10 @@ public abstract class Translate {
 
     /** lang in routerconsole.lang property, else current locale */
     public static String getString(String key, I2PAppContext ctx, String bun) {
+        if (key == null) {
+            (new NullPointerException("null translation string")).printStackTrace();
+            return "";
+        }
         String lang = getLanguage(ctx);
         if (lang.equals("en"))
             return key;