Google Apps Script range getValues returns null if any cell contains a date

I'm trying to get the range values. I noticed, if any range cell contains a date value (for example, 2000-01-01), getValues() returns null:

SpreadsheetApp.getActiveSpreadsheet().getRangeByName('MY_NAMED_RANGE').getValues();

But when using getDisplayValues() I get the values no problem

SpreadsheetApp.getActiveSpreadsheet().getRangeByName('MY_NAMED_RANGE').getDisplayValues();

Is it a bug of getValues()?
I need to get the precise/unformatted values, so I cannot use getDisplayValues()

Thanks in advance for your help!

Thank you all for your replies. I'm trying to get some named range data in my Google Sheets custom sidebar, here is my simplified example:

So I use this (backend) Google Script function (getting the values of a named range):

function gsExplorationData(){
    var range=SpreadsheetApp.getActiveSpreadsheet().getRangeByName('MyNamedRange');
    Logger.log({'range.getValues()': range.getValues()});
    return {'range.getValues()': range.getValues()}
}

Here is my Sidebar javascript function:

dataSubmit(){
  google.script.run.withFailureHandler(function(error){console.log('GS ERROR: '+ error.message)}).withSuccessHandler(function(gsResponse){
    console.log('gsExplorationData()',gsResponse);
  }).gsGetgsExplorationDataData()
}

When running dataSubmit() I see the results fine in the Executions logs:
cloud logs

BUT the dataSubmit() outputs null in the DEV tools:
getting Null in the sidebar javascript

Now if I simply remove the date value in Cell B16 from my named range, I get the range values in the sidebar javascript function no problem:
no date values

Or if change my google script function to return getDisplayValue(), it also works:

function gsExplorationData(){
    var range=SpreadsheetApp.getActiveSpreadsheet().getRangeByName('MyNamedRange');
    Logger.log({'range.getValues()': range.getValues()});
    return {'range.getDisplayValues()': range.getDisplayValues()}
}

getDisplayValues

It also works if I stringify getValues:

function gsExplorationData(){
    var range=SpreadsheetApp.getActiveSpreadsheet().getRangeByName('MyNamedRange');
    Logger.log({'range.getValues()': range.getValues()});
    return {'range.getValues() stringified': JSON.stringify(range.getValues())}
}

stringified values

So the issue is with getting the range getValues() results (that contain date values) from a Google Sheets function in a sidebar javascript function.

UPDATE: kudos to @Daniel who pointed out to the limitations of Apps Script, in particular when returning Dates from Google Script functions called using google.script.run

> This has been reported in Google's issue tracker in the past, but it
> has been marked as "Intended behavior", so it seems that there are no
> plans to add this functionality at the moment. It could be a limit of
> how the Apps Script client-to-server communication works, or some kind
> of security measure.
>
> As a workaround you can try to pass the dates as raw strings, and then
> convert them to Date objects on the client-side.
>
> Reference: HTML Service: Communicate with Server Functions

I checked your sample code, and this is a limitation of trying to pass the values to the sidebar with google.script.run. From the documentation:

>Legal parameters and return values are JavaScript primitives like a Number, Boolean, String, or null, as well as JavaScript objects and arrays that are composed of primitives, objects and arrays.
>
>(...)
>
>Requests fail if you attempt to pass a Date, Function, DOM element besides a form, or other prohibited type, including prohibited types inside objects or arrays.

This has been reported in Google's issue tracker in the past, but it has been marked as "Intended behavior", so it seems that there are no plans to add this functionality at the moment. It could be a limit of how the Apps Script client-to-server communication works, or some kind of security measure.

As a workaround you can try to pass the dates as raw strings, and then convert them to Date objects on the client-side.

Reference:

• HTML Service: Communicate with Server Functions