Fix null literal

resources/bytecode/javFiles/Literal.jav

@@ -0,0 +1,3 @@
+public class Literal {
+    m() { return null; }
+}

src/main/java/de/dhbwstuttgart/bytecode/Codegen.java

@@ -806,6 +806,7 @@ public class Codegen {
                 case StringLiteral stringLiteral -> mv.visitLdcInsn(stringLiteral.value());
                 case CharLiteral charLiteral -> mv.visitIntInsn(BIPUSH, charLiteral.value());
                 case DoubleLiteral doubleLiteral -> mv.visitLdcInsn(doubleLiteral.value());
+                case Null ignored -> mv.visitInsn(ACONST_NULL);
                 case BooleanLiteral booleanLiteral -> {
                     if (booleanLiteral.value()) {
                         mv.visitInsn(ICONST_1);

src/main/java/de/dhbwstuttgart/target/generate/StatementToTargetExpression.java

@@ -320,6 +320,8 @@ public class StatementToTargetExpression implements ASTVisitor {
             result = new TargetLiteral.StringLiteral((String) literal.value);
         } else if (literal.value instanceof Boolean) {
             result = new TargetLiteral.BooleanLiteral((boolean) literal.value);
+        } else if (literal.value == null) {
+            result = new TargetLiteral.Null();
         }
     }
 

src/main/java/de/dhbwstuttgart/target/tree/expression/TargetLiteral.java

@@ -53,4 +53,16 @@ public sealed interface TargetLiteral extends TargetExpression {
             return TargetType.String;
         }
     }
+
+    record Null() implements TargetLiteral {
+        @Override
+        public TargetType type() {
+            return TargetType.Object;
+        }
+
+        @Override
+        public Object value() {
+            return null;
+        }
+    }
 }

src/main/java/de/dhbwstuttgart/typeinference/typeAlgo/TYPEStmt.java

@@ -451,7 +451,8 @@ public class TYPEStmt implements StatementVisitor {
         if (literal.value instanceof Boolean) {
             constraintsSet.addUndConstraint(new Pair(literal.getType(), bool, PairOperator.EQUALSDOT));
             return;
-        } else {
+        }
+        if (literal.value != null) {
             throw new NotImplementedException();
         }
     }

src/test/java/TestComplete.java

@@ -816,4 +816,13 @@ public class TestComplete {
             }
         }
     }
+
+    @Test
+    public void testLiteral() throws Exception {
+        var classFiles = generateClassFiles(new ByteArrayClassLoader(), "Literal.jav");
+        var clazz = classFiles.get("Literal");
+        var instance = clazz.getDeclaredConstructor().newInstance();
+
+        assertNull(clazz.getDeclaredMethod("m").invoke(instance));
+    }
 }