diff --git a/DOCUMENTATION.md b/DOCUMENTATION.md
index 26b58622..e08d19f8 100644
--- a/DOCUMENTATION.md
+++ b/DOCUMENTATION.md
@@ -3109,7 +3109,7 @@ type MembersUpdateParamsUser struct {
 ```
 
 <a name="Membership"></a>
-## type [Membership](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L20-L52>)
+## type [Membership](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L19-L51>)
 
 A membership associates a user with a resource, memberships is defined by user, resource, resource type, and associated roles.
 
@@ -3150,7 +3150,7 @@ type Membership struct {
 ```
 
 <a name="MembershipResource"></a>
-## type [MembershipResource](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L55-L75>)
+## type [MembershipResource](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L54-L74>)
 
 Information about the resource the membership is in.
 
@@ -3249,7 +3249,7 @@ type MembershipUserClassic struct {
 ```
 
 <a name="MembershipsClient"></a>
-## type [MembershipsClient](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L182-L184>)
+## type [MembershipsClient](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L175-L177>)
 
 MembershipsClient provides access to the Memberships API.
 
@@ -3262,7 +3262,7 @@ type MembershipsClient struct {
 ```
 
 <a name="NewMembershipsClient"></a>
-### func [NewMembershipsClient](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L186>)
+### func [NewMembershipsClient](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L179>)
 
 ```go
 func NewMembershipsClient(c *client.Client) *MembershipsClient
@@ -3271,7 +3271,7 @@ func NewMembershipsClient(c *client.Client) *MembershipsClient
 
 
 <a name="MembershipsClient.List"></a>
-### func \(\*MembershipsClient\) [List](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L191>)
+### func \(\*MembershipsClient\) [List](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L184>)
 
 ```go
 func (c *MembershipsClient) List(ctx context.Context, params MembershipsListParams) (*MembershipsListResponse, error)
@@ -3280,7 +3280,7 @@ func (c *MembershipsClient) List(ctx context.Context, params MembershipsListPara
 List memberships of the current user.
 
 <a name="MembershipsListParams"></a>
-## type [MembershipsListParams](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L84-L111>)
+## type [MembershipsListParams](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L83-L112>)
 
 MembershipsListParams are query parameters for ListMemberships.
 
@@ -3299,13 +3299,15 @@ type MembershipsListParams struct {
     // Filter memberships by the name of the resource the membership is in.
     ResourceName *string
     // Filter memberships by the parent of the resource the membership is in.
-    // When filtering by parent both `resource.parent.id` and `resource.parent.type` must be present. Pass explicit null
-    // to filter for resources without a parent.
-    ResourceParentID *nullable.Field[string]
+    // Omit both `resource.parent.id` and `resource.parent.type` to skip parent filtering. When filtering by parent,
+    // both parameters must be present. To select resources without a parent, set each parameter to an empty value.
+    // Otherwise, both parameters must identify a parent.
+    ResourceParentID *string
     // Filter memberships by the parent of the resource the membership is in.
-    // When filtering by parent both `resource.parent.id` and `resource.parent.type` must be present. Pass explicit null
-    // to filter for resources without a parent.
-    ResourceParentType *nullable.Field[ResourceType]
+    // Omit both `resource.parent.id` and `resource.parent.type` to skip parent filtering. When filtering by parent,
+    // both parameters must be present. To select resources without a parent, set each parameter to an empty value.
+    // Otherwise, both parameters must identify a parent.
+    ResourceParentType *ResourceType
     // Filter memberships by resource kind.
     ResourceType *ResourceType
     // Filter the returned memberships by role.
@@ -3316,7 +3318,7 @@ type MembershipsListParams struct {
 ```
 
 <a name="MembershipsListParams.QueryValues"></a>
-### func \(\*MembershipsListParams\) [QueryValues](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L114>)
+### func \(\*MembershipsListParams\) [QueryValues](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L115>)
 
 ```go
 func (p *MembershipsListParams) QueryValues() url.Values
@@ -3325,7 +3327,7 @@ func (p *MembershipsListParams) QueryValues() url.Values
 QueryValues converts [MembershipsListParams](<#MembershipsListParams>) into \[url.Values\].
 
 <a name="MembershipsListResponse"></a>
-## type [MembershipsListResponse](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L173-L176>)
+## type [MembershipsListResponse](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L166-L169>)
 
 MembershipsListResponse is a schema definition.
 
@@ -4816,7 +4818,7 @@ func (p *ReceiptsGetParams) QueryValues() url.Values
 QueryValues converts [ReceiptsGetParams](<#ReceiptsGetParams>) into \[url.Values\].
 
 <a name="ResourceType"></a>
-## type [ResourceType](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L81>)
+## type [ResourceType](<https://github.com/sumup/sumup-go/blob/main/memberships.go#L80>)
 
 The type of the membership resource. Possible values are: \* \`merchant\` \- merchant account\(s\) \* \`organization\` \- organization\(s\)
 
diff --git a/internal/cmd/codegen/pkg/builder/transform.go b/internal/cmd/codegen/pkg/builder/transform.go
index f418aa56..0939d40a 100644
--- a/internal/cmd/codegen/pkg/builder/transform.go
+++ b/internal/cmd/codegen/pkg/builder/transform.go
@@ -174,10 +174,6 @@ func (b *Builder) pathsToParamTypes(tagName string, paths *v3.Paths) []Writable
 
 					optional := param.Required == nil || !*param.Required
 					pointer := shouldUsePointer(optional, param.Schema, typ)
-					if isNullableSchema(param.Schema) {
-						typ = "nullable.Field[" + typ + "]"
-						pointer = optional
-					}
 					fields = append(fields, StructField{
 						Name:      name,
 						Type:      typ,
diff --git a/internal/cmd/codegen/pkg/builder/types.go b/internal/cmd/codegen/pkg/builder/types.go
index 9ad5877c..34ca919a 100644
--- a/internal/cmd/codegen/pkg/builder/types.go
+++ b/internal/cmd/codegen/pkg/builder/types.go
@@ -276,27 +276,7 @@ func (e toQueryValues) String() string {
 	fmt.Fprintf(buf, "\tq := make(url.Values)\n\n")
 	for _, f := range e.Typ.Fields {
 		name := strcase.ToCamel(f.Name)
-		if isNullableSchema(f.Parameter.Schema) {
-			field := fmt.Sprintf("p.%s", name)
-			if f.Pointer {
-				fmt.Fprintf(buf, "\tif %s != nil {\n", field)
-			}
-			fmt.Fprintf(buf, "\tif %s.Null() {\n", field)
-			fmt.Fprintf(buf, "\t\tq.Set(%q, %q)\n", f.Name, "null")
-			fmt.Fprint(buf, "\t} else {\n")
-			schema := dereferenceSchema(f.Parameter.Schema)
-			if schema != nil && schema.Schema() != nil && isArraySchema(schema.Schema()) {
-				fmt.Fprintf(buf, "\t\tfor _, v := range *%s.Value() {\n", field)
-				fmt.Fprintf(buf, "\t\t\tq.Add(%q, %s)\n", f.Name, schemaToString("v", schema.Schema().Items.A))
-				fmt.Fprint(buf, "\t\t}\n")
-			} else {
-				fmt.Fprintf(buf, "\t\tq.Set(%q, %s)\n", f.Name, paramToString("*"+field+".Value()", f.Parameter))
-			}
-			fmt.Fprint(buf, "\t}\n")
-			if f.Pointer {
-				fmt.Fprint(buf, "\t}\n")
-			}
-		} else if f.Parameter.Schema != nil && f.Parameter.Schema.Schema() != nil && slices.Contains(f.Parameter.Schema.Schema().Type, "array") {
+		if f.Parameter.Schema != nil && f.Parameter.Schema.Schema() != nil && slices.Contains(f.Parameter.Schema.Schema().Type, "array") {
 			field := fmt.Sprintf("p.%s", name)
 			fmt.Fprintf(buf, "\tfor _, v := range %s {\n", field)
 			fmt.Fprintf(buf, "\t\tq.Add(%q, %s)\n", f.Name, paramToString("v", f.Parameter))
diff --git a/memberships.go b/memberships.go
index a191dbb1..55ccd8e0 100755
--- a/memberships.go
+++ b/memberships.go
@@ -12,7 +12,6 @@ import (
 	"time"
 
 	"github.com/sumup/sumup-go/client"
-	"github.com/sumup/sumup-go/nullable"
 )
 
 // A membership associates a user with a resource, memberships is defined by user, resource, resource type, and
@@ -95,13 +94,15 @@ type MembershipsListParams struct {
 	// Filter memberships by the name of the resource the membership is in.
 	ResourceName *string
 	// Filter memberships by the parent of the resource the membership is in.
-	// When filtering by parent both `resource.parent.id` and `resource.parent.type` must be present. Pass explicit null
-	// to filter for resources without a parent.
-	ResourceParentID *nullable.Field[string]
+	// Omit both `resource.parent.id` and `resource.parent.type` to skip parent filtering. When filtering by parent,
+	// both parameters must be present. To select resources without a parent, set each parameter to an empty value.
+	// Otherwise, both parameters must identify a parent.
+	ResourceParentID *string
 	// Filter memberships by the parent of the resource the membership is in.
-	// When filtering by parent both `resource.parent.id` and `resource.parent.type` must be present. Pass explicit null
-	// to filter for resources without a parent.
-	ResourceParentType *nullable.Field[ResourceType]
+	// Omit both `resource.parent.id` and `resource.parent.type` to skip parent filtering. When filtering by parent,
+	// both parameters must be present. To select resources without a parent, set each parameter to an empty value.
+	// Otherwise, both parameters must identify a parent.
+	ResourceParentType *ResourceType
 	// Filter memberships by resource kind.
 	ResourceType *ResourceType
 	// Filter the returned memberships by role.
@@ -139,19 +140,11 @@ func (p *MembershipsListParams) QueryValues() url.Values {
 	}
 
 	if p.ResourceParentID != nil {
-		if p.ResourceParentID.Null() {
-			q.Set("resource.parent.id", "null")
-		} else {
-			q.Set("resource.parent.id", *p.ResourceParentID.Value())
-		}
+		q.Set("resource.parent.id", *p.ResourceParentID)
 	}
 
 	if p.ResourceParentType != nil {
-		if p.ResourceParentType.Null() {
-			q.Set("resource.parent.type", "null")
-		} else {
-			q.Set("resource.parent.type", string(*p.ResourceParentType.Value()))
-		}
+		q.Set("resource.parent.type", string(*p.ResourceParentType))
 	}
 
 	if p.ResourceType != nil {
diff --git a/openapi.json b/openapi.json
index 0c914234..8f2f6618 100644
--- a/openapi.json
+++ b/openapi.json
@@ -3454,27 +3454,19 @@
           {
             "name": "resource.parent.id",
             "in": "query",
-            "description": "Filter memberships by the parent of the resource the membership is in.\nWhen filtering by parent both `resource.parent.id` and `resource.parent.type` must be present. Pass explicit null to filter for resources without a parent.",
+            "allowEmptyValue": true,
+            "description": "Filter memberships by the parent of the resource the membership is in.\nOmit both `resource.parent.id` and `resource.parent.type` to skip parent filtering. When filtering by parent, both parameters must be present. To select resources without a parent, set each parameter to an empty value. Otherwise, both parameters must identify a parent.",
             "schema": {
-              "type": [
-                "string",
-                "null"
-              ]
+              "type": "string"
             }
           },
           {
             "name": "resource.parent.type",
             "in": "query",
-            "description": "Filter memberships by the parent of the resource the membership is in.\nWhen filtering by parent both `resource.parent.id` and `resource.parent.type` must be present. Pass explicit null to filter for resources without a parent.",
+            "allowEmptyValue": true,
+            "description": "Filter memberships by the parent of the resource the membership is in.\nOmit both `resource.parent.id` and `resource.parent.type` to skip parent filtering. When filtering by parent, both parameters must be present. To select resources without a parent, set each parameter to an empty value. Otherwise, both parameters must identify a parent.",
             "schema": {
-              "anyOf": [
-                {
-                  "$ref": "#/components/schemas/ResourceType"
-                },
-                {
-                  "type": "null"
-                }
-              ]
+              "$ref": "#/components/schemas/ResourceType"
             }
           },
           {