Bug fixes

Author: dibyendumajumdar

optvm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java

@@ -613,7 +613,7 @@ public void testMergeSort() {
         String src = """
 // based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
 // via https://github.com/SeaOfNodes/Simple
-func merge_sort(a: [Int], b: [int], n: Int) 
+func merge_sort(a: [Int], b: [Int], n: Int) 
 {
     copy_array(a, 0, n, b)
     split_merge(a, 0, n, b)

registervm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java

@@ -250,7 +250,7 @@ public void testMergeSort() {
         String src = """
 // based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
 // via https://github.com/SeaOfNodes/Simple
-func merge_sort(a: [Int], b: [int], n: Int) 
+func merge_sort(a: [Int], b: [Int], n: Int) 
 {
     copy_array(a, 0, n, b)
     split_merge(a, 0, n, b)

seaofnodes/src/main/java/com/compilerprogramming/ezlang/compiler/Compiler.java

@@ -941,7 +941,11 @@ private Node compileLet(AST.VarStmt letStmt) {
     }
 
     private Node compileReturn(AST.ReturnStmt returnStmt) {
-        var expr = compileExpr(returnStmt.expr);
+        Node expr;
+        if (returnStmt.expr != null)
+            expr = compileExpr(returnStmt.expr);
+        else
+            expr = ZERO;
         // Need default memory, since it can be lazy, need to force
         // a non-lazy Phi
         _fun.addReturn(ctrl(), _scope.mem().merge(), expr);