Missing LocalPluginContext , LocalPluginContext not fou

protected void ExecuteYourPlugin(LocalPluginContext localContext)
{
    IPluginExecutionContext pluginContext = localContext.PluginExecutionContext;
    // Get Target Entity
    var updateEntity = (Entity)pluginContext.InputParameters["Target"];

    // Get PreImage Entity
    var preEntity = (Entity)localContext.PluginExecutionContext.PreEntityImages["PreImage"];

    // Is in Update
    if(localContext.PluginExecutionContext.MessageName.ToLower() == "update")
    {
        var fieldName = string.Empty;

            // If Contains, Extract value from Target Entity
            if(updateEntity.Contains("new_fieldname"))
            {
                // Cast the fields according their type
                fieldName = updateEntity["new_fieldname"].toString();
            }
            // Else extract the value from preImage
            else if(preEntity .Contains("new_fieldname"))
            {
                // Cast the fields according their type
                fieldName = preEntity["new_fieldname"].toString();
            }
    }