Thank you for reporting the bug. Please attach a sample document, as this makes it easier for us to verify the bug. 
I have set the bug's status to 'NEEDINFO'. Please change it back to 'UNCONFIRMED' once the requested document is provided.
(Please note that the attachment will be public, remove any sensitive information before attaching it. 
See https://wiki.documentfoundation.org/QA/FAQ#How_can_I_eliminate_confidential_data_from_a_sample_document.3F for help on how to do so.)

BTW, this is the LibreOffice's bugzilla, not the OpenOffice's one...

Created attachment 136054 [details]
Exemples preadsheet with bugged chart

As requested I attached a spreadsheet exemple.

Sorry to have confused you with OO. You are way better.

When I open your file with excel 2010, I get error message. The file doesn't seem to be valid.

Please provide clear steps how to reproduce the bug. Thank you

I had no problem to open the file either with LibreOffice or Excel 2013+. Could you try again.

The bug happens when loading a .xlsx spreadsheet modified in LibreOffice with the openpyxl module in python. 

1. Creating a chart in a sperate tab
2. Deleting the chart
3. Saving the file
4. Importing with openpyxl in python

(In reply to raal from comment #4)
> When I open your file with excel 2010, I get error message. The file doesn't
> seem to be valid.

Same behaviour here... Probably one of those files which are incompatible among different versions of MSO ?

(In reply to Marc Oggier from comment #2)
> Created attachment 136054 [details]
> Exemples preadsheet with bugged chart

So this file was originally created in what program?
Then the error you talk about is raised by openpyxl, right?

1.a The original file was created with Excel, reopen with LibreOffice, save via OpenOffice and then imported with openpyxl. The error happened.
1.b I created a file with LibreOffice with the same template. The error happened again.

2.a Yes the error raised when opening the file with openpyxl.
2.b I filed a bug report at openpyxl, which added a temporary fix to it. You can find they answer via the following line. (https://bitbucket.org/openpyxl/openpyxl/issues/885/loading-workbook-error-float-argument-must)

Hmm, yeah, I think we can count the analysis of openpyxl dev as confirmation, so setting to NEW.

(In reply to Buovjaga from comment #9)
> Hmm, yeah, I think we can count the analysis of openpyxl dev as
> confirmation, so setting to NEW.

Well - I don't think we can count that analysis as a confirmation, until we have a proper report with steps to reproduce.

The bug title is "empty values in y-axis of empty chart".
The comment 0 starts with a sentence mentioning "a xlsx spreadsheet, containing a chart", but no normal steps.
The comment 5 has this:

> 1. Creating a chart in a sperate tab
> 2. Deleting the chart
... which gives us a spreadsheet *without* a chart.

Trying to recreate something out of this gives me nothing. My attempts included:
1. Opening initial file to check if it contained some charts (no);
2. Saving the original file in LO to find if LO writes something like  comment 0 in this case (no; by the way, the saved file doesn't produce errors in Excel 2016, unlike the original);
3. Creating a chart on a separate sheet, with nothing selected (produces an empty chart), and deleting it (literally following comment 5), then saving and looking if it has a chart XML (no);
4. The same as in 3, but without deletion of the chart; the result does contain a chart XML, but no <c:v>s at all;
5. As in 4, but select some range (like A1:B2) on the empty sheet prior to chart creation, and then deleting the single series in the chart (the result is the same as in 4).

Further, ECMA-376-1:2016 [1] only mentions "NumVal" as "CT_NumVal" for 21.2.2.150 pt (Numeric Point); but the standard puts just one single requirement to the included c:v element, which is

> <xsd:simpleType name="ST_Xstring">
> <xsd:restriction base="xsd:string"/>
> </xsd:simpleType>

... so no requirement to put some numeric value there.
This makes me wonder if an "analisys" that mentions such requirements in the standard, and then stating things like "but really seems to be a wart in LibreOffice", is something capable to confirm this report.

[1] https://www.ecma-international.org/publications/standards/Ecma-376.htm

Fair enough.
Marc: can you involve the openpyxl dev in this conversation again? Thanks.

(In reply to Buovjaga from comment #13)
> Fair enough.
> Marc: can you involve the openpyxl dev in this conversation again? Thanks.

No need to put it in NEEDINFO...

I will have a look if the bug is still present and involve openpyxl dev if it is.

(In reply to Xisco Faulí from comment #14)
> (In reply to Buovjaga from comment #13)
> > Fair enough.
> > Marc: can you involve the openpyxl dev in this conversation again? Thanks.
> 
> No need to put it in NEEDINFO...

As

This bug needs clear steps responding to Comment 11 and 12.

Dear Marc Oggier,

Please read this message in its entirety before proceeding.

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