tiny fix

src/main/java/chocopy/pa3/CodeGenImpl.java

@@ -699,8 +699,7 @@ public class CodeGenImpl extends CodeGenBase {
             // Label nonError = generateLocalLabel();
             if (id.getInferredType() instanceof ClassValueType 
             && !id.getInferredType().equals(SymbolType.INT_TYPE) 
-            && !id.getInferredType().equals(SymbolType.BOOL_TYPE)
-            && !id.getInferredType().equals(SymbolType.STR_TYPE)) {
+            && !id.getInferredType().equals(SymbolType.BOOL_TYPE)) {
                 backend.emitBEQZ(tmpReg, errorNone, "CHECK: Object is non-null");
                 //backend.emitJ(errorNone, "Jump to None error handler");
                 //backend.emitLocalLabel(nonError, "Object is non-null");