Initialize local variables to null

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

@@ -810,6 +810,9 @@ public class Codegen {
                     generate(state, varDecl.value());
                     boxPrimitive(state, varDecl.varType());
                     mv.visitVarInsn(ASTORE, local.index());
+                } else {
+                    mv.visitInsn(ACONST_NULL);
+                    mv.visitVarInsn(ASTORE, local.index());
                 }
                 break;
             }