[truffle] Implement nqp::null_s

Author: pmurias

src/vm/jvm/Truffle.nqp

@@ -148,6 +148,8 @@ class QAST::OperationsTruffle {
 
     add_simple_op('null', $OBJ, []);
 
+    add_simple_op('null_s', $STR, []);
+
     add_simple_op('concat', $STR, [$STR, $STR]);
 
     add_simple_op('lc', $STR, [$STR]);

src/vm/jvm/runtime/org/perl6/nqp/truffle/nodes/expression/NQPNullStrNode.java

@@ -0,0 +1,19 @@
+package org.perl6.nqp.truffle.nodes.expression;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import org.perl6.nqp.truffle.nodes.NQPNode;
+import org.perl6.nqp.truffle.nodes.NQPStrNode;
+import org.perl6.nqp.dsl.Deserializer;
+
+@NodeInfo(shortName = "null_s")
+public final class NQPNullStrNode extends NQPStrNode {
+
+    @Deserializer
+    public NQPNullStrNode() {
+    }
+
+    @Override
+    public String executeStr(VirtualFrame frame) {
+        return null;
+    }
+}