Share a common array for empty keyword arguments.

Author: nirvdrum

src/main/java/org/truffleruby/core/symbol/RubySymbol.java

@@ -40,6 +40,8 @@ public final class RubySymbol extends ImmutableRubyObjectNotCopyable implements
 
     private static final int CLASS_SALT = 92021474; // random number, stops hashes for similar values but different classes being the same, static because we want deterministic hashes
 
+    public static final RubySymbol[] EMPTY_ARRAY = new RubySymbol[0];
+
     public final RubyEncoding encoding;
     private final String string;
     public final TruffleString tstring;

src/main/java/org/truffleruby/language/arguments/CheckKeywordArityNode.java

@@ -117,6 +117,11 @@ private Object[] findExtraKeywordArguments(RubyHash keywordArguments) {
 
     static RubySymbol[] keywordsAsSymbols(RubyLanguage language, Arity arity) {
         final String[] names = arity.getKeywordArguments();
+
+        if (names.length == 0) {
+            return RubySymbol.EMPTY_ARRAY;
+        }
+
         final RubySymbol[] symbols = new RubySymbol[names.length];
         for (int i = 0; i < names.length; i++) {
             symbols[i] = language.getSymbol(names[i]);