diff --git a/src/OrchardCore.Modules/OrchardCore.ContentTypes/Services/ContentDefinitionService.cs b/src/OrchardCore.Modules/OrchardCore.ContentTypes/Services/ContentDefinitionService.cs
index 401f4e50ad6..660da6d2bab 100644
--- a/src/OrchardCore.Modules/OrchardCore.ContentTypes/Services/ContentDefinitionService.cs
+++ b/src/OrchardCore.Modules/OrchardCore.ContentTypes/Services/ContentDefinitionService.cs
@@ -322,7 +322,7 @@ public async Task AddFieldToPartAsync(string fieldName, string displayName, stri
         {
             if (string.IsNullOrEmpty(fieldName))
             {
-                throw new ArgumentException("The 'fieldName' can't be null or empty.", nameof(fieldName));
+                throw new ArgumentException("The '{fieldName}' can't be null or empty.", nameof(fieldName));
             }
 
             var partDefinition = await _contentDefinitionManager.LoadPartDefinitionAsync(partName);
@@ -390,9 +390,20 @@ await _contentDefinitionManager.AlterTypeDefinitionAsync(typeDefinition.Name, ty
         public Task AlterTypePartsOrderAsync(ContentTypeDefinition typeDefinition, string[] partNames)
             => _contentDefinitionManager.AlterTypeDefinitionAsync(typeDefinition.Name, type =>
             {
+                if (partNames is null)
+                {
+                    return;
+                }
+
                 for (var i = 0; i < partNames.Length; i++)
                 {
-                    var partDefinition = typeDefinition.Parts.FirstOrDefault(x => x.Name == partNames[i]);
+                    var partDefinition = typeDefinition.Parts?.FirstOrDefault(x => x.Name == partNames[i]);
+                    
+                    if (partDefinition == null)
+                    {
+                        continue;
+                    }
+
                     type.WithPart(partNames[i], partDefinition.PartDefinition, part =>
                     {
                         part.MergeSettings<ContentTypePartSettings>(x => x.Position = i.ToString());
@@ -403,6 +414,11 @@ public Task AlterTypePartsOrderAsync(ContentTypeDefinition typeDefinition, strin
         public Task AlterPartFieldsOrderAsync(ContentPartDefinition partDefinition, string[] fieldNames)
             => _contentDefinitionManager.AlterPartDefinitionAsync(partDefinition.Name, type =>
             {
+                if (fieldNames is null)
+                {
+                    return;
+                }
+
                 for (var i = 0; i < fieldNames.Length; i++)
                 {
                     var fieldDefinition = partDefinition.Fields.FirstOrDefault(x => x.Name == fieldNames[i]);
@@ -437,9 +453,9 @@ public async Task<string> GenerateFieldNameFromDisplayNameAsync(string partName,
                 var type = await _contentDefinitionManager.LoadTypeDefinitionAsync(partName)
                     ?? throw new ArgumentException("The part doesn't exist: " + partName);
 
-                var typePart = type.Parts.FirstOrDefault(x => x.PartDefinition.Name == partName);
+                var typePart = type.Parts?.FirstOrDefault(x => x.PartDefinition.Name == partName);
 
-                // Id passed in might be that of a type w/ no implicit field.
+                // If passed in might be that of a type w/ no implicit field.
                 if (typePart == null)
                 {
                     return displayName;