Repository: dotnet/aspnetcore
File: src/Features/JsonPatch.SystemTextJson/src/Internal/ListAdapter.cs (C#)

Code before:
            return false;
        }

        var currentValue = GenericListOrJsonArrayUtilities.GetElementAt(target, positionInfo.Index);

        if (!JsonUtilities.DeepEquals(currentValue, convertedValue, serializerOptions))
        {
            errorMessage = Resources.FormatValueAtListPositionNotEqualToTestValue(currentValue, value, positionInfo.Index);
            return false;
        }
        else
        {
            errorMessage = null;
            return true;
        }
    }

    public virtual bool TryTraverse(object target, string segment, JsonSerializerOptions serializerOptions, out object value, out string errorMessage)
    {
        if(!TryGetListTypeArgument(target, out _, out errorMessage))
        {
            value = null;
            return false;
        }

        var count = GenericListOrJsonArrayUtilities.GetCount(target);

        if (!int.TryParse(segment, out var index))
        {
            value = null;
            errorMessage = Resources.FormatInvalidIndexValue(segment);
            return false;
        }

        if (index < 0 || index >= count)
        {
            value = null;
            errorMessage = Resources.FormatIndexOutOfBounds(segment);
            return false;
        }

        value = GenericListOrJsonArrayUtilities.GetElementAt(target, index);
        errorMessage = null;
        return true;
    }

    protected virtual bool TryConvertValue(object originalValue, Type listTypeArgument, string segment, out object convertedValue, out string errorMessage)
    {
        return TryConvertValue(originalValue, listTypeArgument, segment, null, out convertedValue, out errorMessage);
    }


Review comment (suggestion):
This could be moved down after this if check and maybe even inlined into the if where it is actually checked, so the code is only executed when necessary.

Code after:
            return false;
        }

        var currentValue = GenericListOrJsonArrayUtilities.GetElementAt(target, positionInfo.Index);

        if (!JsonUtilities.DeepEquals(currentValue, convertedValue, serializerOptions))
        {
            errorMessage = Resources.FormatValueAtListPositionNotEqualToTestValue(currentValue, value, positionInfo.Index);
            return false;
        }
        else
        {
            errorMessage = null;
            return true;
        }
    }

    public virtual bool TryTraverse(object target, string segment, JsonSerializerOptions serializerOptions, out object value, out string errorMessage)
    {
        if (!TryGetListTypeArgument(target, out _, out errorMessage))
        {
            value = null;
            return false;
        }

        if (!int.TryParse(segment, out var index))
        {
            value = null;
            errorMessage = Resources.FormatInvalidIndexValue(segment);
            return false;
        }

        var count = GenericListOrJsonArrayUtilities.GetCount(target);

        if (index < 0 || index >= count)
        {
            value = null;
            errorMessage = Resources.FormatIndexOutOfBounds(segment);
            return false;
        }

        value = GenericListOrJsonArrayUtilities.GetElementAt(target, index);
        errorMessage = null;
        return true;
    }

    protected virtual bool TryConvertValue(object originalValue, Type listTypeArgument, string segment, out object convertedValue, out string errorMessage)
    {
        return TryConvertValue(originalValue, listTypeArgument, segment, null, out convertedValue, out errorMessage);
    }