'Ambiguous reference' error

[Koen Laan]

I have the latest Curvy but still the same error
also unity 2018.3

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do I only need to adjust the cs code in the MinDrawer.cs? or anywhere else?
Could you tell me where to change the code?
ps love Curvy (obvious without the bug)

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in my code: MinDrawer.cs I have the following code:

using UnityEngine;
using UnityEngine.PostProcessing;

namespace UnityEditor.PostProcessing
{
[CustomPropertyDrawer(typeof(MinAttribute))]
sealed class MinDrawer : PropertyDrawer
{
public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
{
MinAttribute attribute = (MinAttribute)base.attribute;

if (property.propertyType == SerializedPropertyType.Integer)
{
int v = EditorGUI.IntField(position, label, property.intValue);
property.intValue = (int)Mathf.Max(v, attribute.min);
}
else if (property.propertyType == SerializedPropertyType.Float)
{
float v = EditorGUI.FloatField(position, label, property.floatValue);
property.floatValue = Mathf.Max(v, attribute.min);
}
else
{
EditorGUI.LabelField(position, label.text, "Use Min with float or int.");
}
}
}
}