[GR-40549] Return EMPTY_US_ASCII for TStringConstants.lookupUSASCIITString("")

PullRequest: truffleruby/3485

Author: eregon

src/main/java/org/truffleruby/core/string/TStringConstants.java

@@ -220,7 +220,9 @@ private static TruffleString ascii(String string) {
     }
 
     public static TruffleString lookupUSASCIITString(String string) {
-        if (string.length() == 1) {
+        if (string.isEmpty()) {
+            return EMPTY_US_ASCII;
+        } else if (string.length() == 1) {
             return US_ASCII_SINGLE_BYTE[string.charAt(0)];
         } else {
             return TSTRING_CONSTANTS.get(string);

src/main/java/org/truffleruby/debug/TruffleDebugNodes.java

@@ -273,8 +273,7 @@ public abstract static class ASTNode extends CoreMethodArrayArgumentsNode {
         protected Object ast(Object executable,
                 @Cached ToCallTargetNode toCallTargetNode) {
             final RootCallTarget callTarget = toCallTargetNode.execute(executable);
-            ast(callTarget.getRootNode());
-            return nil;
+            return ast(callTarget.getRootNode());
         }
 
         private Object ast(Node node) {