fix: handle nil zeroer pointers in Option.IsZero

option.go

@@ -252,14 +252,19 @@ func (o Option[T]) IsZero() bool {
 		return true
 	}
 
+	// A nil pointer can implement zeroer through a value-receiver method,
+	// which cannot be called without dereferencing the nil pointer.
+	rv := reflect.ValueOf(o.value)
+	if !rv.IsValid() || rv.Kind() == reflect.Ptr && rv.IsNil() {
+		return true
+	}
+
 	var v any = o.value
 	if v, ok := v.(zeroer); ok {
 		return v.IsZero()
 	}
 
-	// a nil interface yields an invalid reflect.Value, on which IsZero panics
-	rv := reflect.ValueOf(o.value)
-	return !rv.IsValid() || rv.IsZero()
+	return rv.IsZero()
 }
 
 // MarshalText implements the encoding.TextMarshaler interface.

option_nil_zero_test.go

@@ -0,0 +1,23 @@
+package mo
+
+import (
+	"testing"
+	"time"
+)
+
+func TestOptionIsZeroNilZeroer(t *testing.T) {
+	var value *time.Time
+	if !Some(value).IsZero() {
+		t.Error("a nil time pointer should be zero")
+	}
+	if !Some[any](value).IsZero() {
+		t.Error("an interface holding a nil time pointer should be zero")
+	}
+	if !Some(&time.Time{}).IsZero() {
+		t.Error("a pointer to zero time should still use time.IsZero")
+	}
+	nonzero := time.Unix(1, 0)
+	if Some(&nonzero).IsZero() {
+		t.Error("a nonzero time pointer should not be zero")
+	}
+}