diff --git a/guinep/src/main/scala/macros.scala b/guinep/src/main/scala/macros.scala
index d0426b9..368e8e0 100644
--- a/guinep/src/main/scala/macros.scala
+++ b/guinep/src/main/scala/macros.scala
@@ -141,6 +141,12 @@ private[guinep] object macros {
         FormElement.FloatingNumberInput(paramName, Types.FloatingType.Double)
       case AppliedType(ntpe: NamedType, List(tpeArg)) if listLikeSymbolsTypes.contains(ntpe.typeSymbol) =>
         FormElement.ListInput(paramName, functionFormElementFromTreeWithCaching("elem", tpeArg), listLikeSymbolsTypes(ntpe.typeSymbol))
+      case OrType(ltpe, rtpe) if ltpe =:= TypeRepr.of[Null] || rtpe =:= TypeRepr.of[Null] =>
+        val innerForm = if ltpe =:= TypeRepr.of[Null] then
+          functionFormElementFromTreeWithCaching(paramName, rtpe)
+        else
+          functionFormElementFromTreeWithCaching(paramName, ltpe)
+        FormElement.Nullable(paramName, innerForm)
       case ntpe if isProductTpe(ntpe) =>
         val classSymbol = ntpe.typeSymbol
         val typeDefParams = classSymbol.primaryConstructor.paramSymss.flatten.filter(_.isTypeParam)
@@ -255,6 +261,9 @@ private[guinep] object macros {
           param.select(s"asInstanceOf").appliedToType(ntpe)
         case AppliedType(ntpe: NamedType, List(tpeArg)) if listLikeSymbolsTypes.contains(ntpe.typeSymbol) =>
           param.select("asInstanceOf").appliedToType(paramTpe)
+        case OrType(ltpe, rtpe) if ltpe =:= TypeRepr.of[Null] || rtpe =:= TypeRepr.of[Null] =>
+          val castedParam = param.select("asInstanceOf").appliedToType(paramTpe)
+          '{ if ${param.asExpr} == null then null else ${castedParam.asExpr} }.asTerm
         case ntpe if isCaseObjectTpe(ntpe) && ntpe.typeSymbol.flags.is(Flags.Module) =>
           Ref(ntpe.typeSymbol.companionModule)
         case ntpe if isCaseObjectTpe(ntpe) =>
diff --git a/guinep/src/main/scala/model.scala b/guinep/src/main/scala/model.scala
index 691df08..26cda6e 100644
--- a/guinep/src/main/scala/model.scala
+++ b/guinep/src/main/scala/model.scala
@@ -47,7 +47,6 @@ private[guinep] object model {
       case List
       case Seq
       case Vector
-      case Array
 
     object ListType:
       given ToExpr[ListType] with
@@ -74,6 +73,7 @@ private[guinep] object model {
     case PasswordInput(override val name: String) extends FormElement(name)
     case FieldSet(override val name: String, elements: List[FormElement]) extends FormElement(name)
     case NamedRef(override val name: String, ref: String) extends FormElement(name)
+    case Nullable(override val name: String, element: FormElement) extends FormElement(name)
 
     def constrOrd: Int = this match
       case TextInput(_) => 0
@@ -89,6 +89,7 @@ private[guinep] object model {
       case PasswordInput(_) => 7
       case FieldSet(_, _) => 8
       case NamedRef(_, _) => 9
+      case Nullable(_, elem) => elem.constrOrd
 
   object FormElement:
     given ToExpr[FormElement] with
@@ -119,6 +120,8 @@ private[guinep] object model {
           '{ FormElement.PasswordInput(${Expr(name)}) }
         case FormElement.NamedRef(name, ref) =>
           '{ FormElement.NamedRef(${Expr(name)}, ${Expr(ref)}) }
+        case FormElement.Nullable(name, element) =>
+          '{ FormElement.Nullable(${Expr(name)}, ${Expr(element)}) }
 
     // This ordering is a hack to avoid placing recursive constructors as first options in a dropdown
     given Ordering[FormElement] = new Ordering[FormElement] {
@@ -130,6 +133,10 @@ private[guinep] object model {
             elems1.size - elems2.size
           case (FormElement.Dropdown(_, opts1), FormElement.Dropdown(_, opts2)) =>
             opts1.size - opts2.size
+          case (FormElement.Nullable(_, elem1), FormElement.Nullable(_, elem2)) =>
+            compare(elem1, elem2)
+          case (FormElement.ListInput(_, elem1, _), FormElement.ListInput(_, elem2, _)) =>
+            compare(elem1, elem2)
           case _ => 0
   }
 }
diff --git a/guinep/src/test/scala/formgentests.scala b/guinep/src/test/scala/formgentests.scala
index ee5af12..4e8eb84 100644
--- a/guinep/src/test/scala/formgentests.scala
+++ b/guinep/src/test/scala/formgentests.scala
@@ -265,6 +265,17 @@ class FormGenTests extends munit.FunSuite {
     )
   )
 
+  checkGeneratedFormEquals(
+    "showNullableInt",
+    showNullableInt,
+    Form(
+      Seq(
+        FormElement.Nullable("i", FormElement.NumberInput("i", Types.IntType.Int))
+      ),
+      Map.empty
+    )
+  )
+
   checkGeneratedFormEquals(
     "isInTree",
     isInTree,
diff --git a/guinep/src/test/scala/rungentests.scala b/guinep/src/test/scala/rungentests.scala
index 8d18ceb..36580d3 100644
--- a/guinep/src/test/scala/rungentests.scala
+++ b/guinep/src/test/scala/rungentests.scala
@@ -207,6 +207,20 @@ class RunGenTests extends munit.FunSuite {
     "6.0"
   )
 
+  checkGeneratedRunResultEquals(
+    "showNullableInt",
+    showNullableInt,
+    List(null),
+    "null"
+  )
+
+  checkGeneratedRunResultEquals(
+    "showNullableInt",
+    showNullableInt,
+    List(1),
+    "1"
+  )
+
   checkGeneratedRunResultEquals(
     "isInTree",
     isInTree,
diff --git a/guinep/src/test/scala/testsdata.scala b/guinep/src/test/scala/testsdata.scala
index 3f7814b..c3838cc 100644
--- a/guinep/src/test/scala/testsdata.scala
+++ b/guinep/src/test/scala/testsdata.scala
@@ -82,6 +82,9 @@ object TestsData {
   def productSeq(s: Seq[Float]): Float =
     s.product
 
+  def showNullableInt(i: Int | Null): String =
+    if i == null then "null" else i.toString
+
   enum IntTree:
     case Leaf
     case Node(left: IntTree, value: Int, right: IntTree)
diff --git a/testcases/src/main/scala/main.scala b/testcases/src/main/scala/main.scala
index 84619fc..ec2caca 100644
--- a/testcases/src/main/scala/main.scala
+++ b/testcases/src/main/scala/main.scala
@@ -102,29 +102,35 @@ def sumVector(v: Vector[Int]): Int =
 def seqProduct(seq: Seq[Float]): Float =
   seq.product
 
+def showNullableInt(i: Int | Null): String =
+  if i == null then "null" else i.toString
+
 @main
 def run: Unit =
-  guinep.web(
-    upperCaseText,
-    add,
-    concat,
-    giveALongText,
-    addObj,
-    greetMaybeName,
-    greetInLanguage,
-    nameWithPossiblePrefix,
-    nameWithPossiblePrefix1,
-    roll20,
-    roll6(),
-    concatAll,
-    showDouble,
-    divideFloats,
-    codeOfChar,
-    isInTree,
-    listProduct,
-    sumVector,
-    seqProduct,
-    // isInTreeExt
-    // addManyParamLists
-    // printsWeirdGADT
-  )
+  guinep.web
+    .withModifyConfig(_.copy(requireNonNullableInputs = true))
+    .apply(
+      upperCaseText,
+      add,
+      concat,
+      giveALongText,
+      addObj,
+      greetMaybeName,
+      greetInLanguage,
+      nameWithPossiblePrefix,
+      nameWithPossiblePrefix1,
+      roll20,
+      roll6(),
+      concatAll,
+      showDouble,
+      divideFloats,
+      codeOfChar,
+      isInTree,
+      listProduct,
+      sumVector,
+      seqProduct,
+      showNullableInt
+      // isInTreeExt
+      // addManyParamLists
+      // printsWeirdGADT
+    )
diff --git a/web/src/main/scala/api.scala b/web/src/main/scala/api.scala
index c7ad39e..6bad335 100644
--- a/web/src/main/scala/api.scala
+++ b/web/src/main/scala/api.scala
@@ -31,10 +31,10 @@ object GuinepWebConfig:
     GuinepWebConfig()
 
 private case class GuinepWeb(config: GuinepWebConfig = GuinepWebConfig.default) {
-  def withSetConfig(config: GuinepWebConfig): Unit =
+  def withSetConfig(config: GuinepWebConfig): GuinepWeb =
     this.copy(config = config)
 
-  def withModifyConfig(f: GuinepWebConfig => GuinepWebConfig): Unit =
+  def withModifyConfig(f: GuinepWebConfig => GuinepWebConfig): GuinepWeb =
     withSetConfig(f(config))
 
   /**
diff --git a/web/src/main/scala/htmlgen.scala b/web/src/main/scala/htmlgen.scala
index 84432de..e32e0ee 100644
--- a/web/src/main/scala/htmlgen.scala
+++ b/web/src/main/scala/htmlgen.scala
@@ -159,6 +159,12 @@ private[guinep] trait HtmlGen {
           input.name = formElem.name;
           input.id = formElem.name;
           input.placeholder = formElem.name;
+          if (formElem.nullable) {
+            input.setAttribute('nullable', formElem.nullable);
+          }
+          if (${config.requireNonNullableInputs} && !formElem.nullable) {
+            input.setAttribute('required', !formElem.nullable);
+          }
           form.insertBefore(input, before);
           form.insertBefore(br.cloneNode(), before);
         } else if (formElem.type == 'char') {
@@ -172,6 +178,12 @@ private[guinep] trait HtmlGen {
           input.name = formElem.name;
           input.id = formElem.name;
           input.placeholder = formElem.name;
+          if (formElem.nullable) {
+            input.setAttribute('nullable', formElem.nullable);
+          }
+          if (${config.requireNonNullableInputs} && !formElem.nullable) {
+            input.setAttribute('required', !formElem.nullable);
+          }
           form.insertBefore(input, before);
           form.insertBefore(br.cloneNode(), before);
         } else {
@@ -184,6 +196,12 @@ private[guinep] trait HtmlGen {
           input.name = formElem.name;
           input.id = formElem.name;
           input.placeholder = formElem.name;
+          if (formElem.nullable) {
+            input.setAttribute('nullable', formElem.nullable);
+          }
+          if (${config.requireNonNullableInputs} && !formElem.nullable) {
+            input.setAttribute('required', !formElem.nullable);
+          }
           form.insertBefore(input, before);
           form.insertBefore(br.cloneNode(), before);
         }
@@ -240,6 +258,8 @@ private[guinep] trait HtmlGen {
             const value = element.value;
             if (element.type === 'checkbox') {
               return [name, element.checked];
+            } else if (element.getAttribute('nullable') && value === '') {
+              return [name, null];
             } else {
               return [name, value];
             }
diff --git a/web/src/main/scala/serialization.scala b/web/src/main/scala/serialization.scala
index 42aa889..f74cfd2 100644
--- a/web/src/main/scala/serialization.scala
+++ b/web/src/main/scala/serialization.scala
@@ -77,45 +77,51 @@ private[guinep] object serialization:
           case guinep.model.Types.ListType.List => res
           case guinep.model.Types.ListType.Seq => res.toSeq
           case guinep.model.Types.ListType.Vector => res.toVector
+      case FormElement.Nullable(_, element) =>
+        value match
+          case Null => Right(null)
+          case _ => element.parseJSONValue(value)
       case _ => Left(s"Unsupported form element: $formElement")
 
   extension (form: Form)
     def formElementsJSONRepr =
-      val elems = form.inputs.map(_.toJSONRepr).mkString(",")
+      val elems = form.inputs.map(_.toJSONRepr()).mkString(",")
       s"[$elems]"
     def namedFormElementsJSONRepr: String =
       val entries = form.namedFormElements.toList.map { (name, formElement) =>
-        s""""$name": ${formElement.toJSONRepr}"""
+        s""""$name": ${formElement.toJSONRepr()}"""
       }
       .mkString(",")
       s"{$entries}"
 
   extension (formElement: FormElement)
-    def toJSONRepr: String = formElement match
+    def toJSONRepr(nullable: Boolean = false): String = formElement match
       case FormElement.FieldSet(name, elements) =>
-        s"""{ "name": '$name', "type": 'fieldset', "elements": [${elements.map(_.toJSONRepr).mkString(",")}] }"""
+        s"""{ "name": '$name', "type": 'fieldset', "elements": [${elements.map(_.toJSONRepr()).mkString(",")}]}"""
       case FormElement.TextInput(name) =>
-        s"""{ "name": '$name', "type": 'text' }"""
+        s"""{ "name": '$name', "type": 'text', "nullable": $nullable }"""
       case FormElement.CharInput(name) =>
-        s"""{ "name": '$name', "type": 'char' }"""
+        s"""{ "name": '$name', "type": 'char', "nullable": $nullable }"""
       case FormElement.NumberInput(name, _) =>
-        s"""{ "name": '$name', "type": 'number' }"""
+        s"""{ "name": '$name', "type": 'number', "nullable": $nullable }"""
       case FormElement.FloatingNumberInput(name, _) =>
-        s"""{ "name": '$name', "type": 'float' }"""
+        s"""{ "name": '$name', "type": 'float', "nullable": $nullable }"""
       case FormElement.CheckboxInput(name) =>
         s"""{ "name": '$name', "type": 'checkbox' }"""
       case FormElement.Dropdown(name, options) =>
         // TODO(kπ) this sortBy isn't 100% sure to be working (the only requirement is for the first constructor to not be recursive; this is a graph problem, sorta)
-        s"""{ "name": '$name', "type": 'dropdown', "options": [${options.sortBy(_._2).map { case (k, v) => s"""{"name": "$k", "value": ${v.toJSONRepr}}""" }.mkString(",")}] }"""
+        s"""{ "name": '$name', "type": 'dropdown', "options": [${options.sortBy(_._2).map { case (k, v) => s"""{"name": "$k", "value": ${v.toJSONRepr()}}""" }.mkString(",")}] }"""
       case FormElement.ListInput(name, element, _) =>
-        s"""{ "name": '$name', "type": 'list', "element": ${element.toJSONRepr} }"""
+        s"""{ "name": '$name', "type": 'list', "element": ${element.toJSONRepr()} }"""
       case FormElement.TextArea(name, rows, cols) =>
-        s"""{ "name": '$name', "type": 'textarea', "rows": ${rows.getOrElse("")}, "cols": ${cols.getOrElse("")} }"""
+        s"""{ "name": '$name', "type": 'textarea', "rows": ${rows.getOrElse("")}, "cols": ${cols.getOrElse("")}, "nullable": $nullable }"""
       case FormElement.DateInput(name) =>
-        s"""{ "name": '$name', "type": 'date' }"""
+        s"""{ "name": '$name', "type": 'date', "nullable": $nullable }"""
       case FormElement.EmailInput(name) =>
-        s"""{ "name": '$name', "type": 'email' }"""
+        s"""{ "name": '$name', "type": 'email', "nullable": $nullable }"""
       case FormElement.PasswordInput(name) =>
-        s"""{ "name": '$name', "type": 'password' }"""
+        s"""{ "name": '$name', "type": 'password', "nullable": $nullable }"""
       case FormElement.NamedRef(name, ref) =>
         s"""{ "name": '$name', "ref": '$ref', "type": 'namedref' }"""
+      case FormElement.Nullable(_, element) =>
+        element.toJSONRepr(nullable = true)