Make sure the empty blocks return nil

Signed-off-by: Stefan Marr <[email protected]>

src/som/compiler/MethodGenerationContext.java

@@ -222,6 +222,10 @@ public void addLocal(final String local) {
     locals.add(local);
   }
 
+  public boolean hasBytecodes() {
+    return !bytecode.isEmpty();
+  }
+
   public void removeLastBytecode() {
     bytecode.remove(bytecode.size() - 1);
   }

src/som/compiler/Parser.java

@@ -456,6 +456,12 @@ private void blockBody(final MethodGenerationContext mgenc, final boolean seenPe
         // was terminated with a . or not)
         mgenc.removeLastBytecode();
       }
+      if (mgenc.isBlockMethod() && !mgenc.hasBytecodes()) {
+        // if the block is empty, we need to return nil
+        SSymbol nilSym = universe.symbolFor("nil");
+        mgenc.addLiteralIfAbsent(nilSym);
+        bcGen.emitPUSHGLOBAL(mgenc, nilSym);
+      }
       bcGen.emitRETURNLOCAL(mgenc);
       mgenc.setFinished();
     } else if (sym == EndTerm) {
@@ -878,6 +884,12 @@ private void nestedBlock(final MethodGenerationContext mgenc) throws ProgramDefi
     // expression
     // in the block was not terminated by ., and can generate a return
     if (!mgenc.isFinished()) {
+      if (!mgenc.hasBytecodes()) {
+        // if the block is empty, we need to return nil
+        SSymbol nilSym = universe.symbolFor("nil");
+        mgenc.addLiteralIfAbsent(nilSym);
+        bcGen.emitPUSHGLOBAL(mgenc, nilSym);
+      }
       bcGen.emitRETURNLOCAL(mgenc);
       mgenc.setFinished(true);
     }