Regarding ODF import and Export support for HistogramChart

[Regina Henschel]

Hi Devansh,

This is wrong:
chart:class="chart:histogram"

"histogram" does not belong to the chart types that are predefined in 
the ODF standard. Only the names of the predefined chart types may have 
a prefix "chart". For chart types not defined in the standard you have 
to use a prefix different from "chart". For chart types defined by 
LibreOffice use the prefix "loext".
So it should be
chart:class="loext:histogram"
in both cases.

This is wrong:
<loext:histogram-configuration loext:histogram-frequency-type="0"
                                loext:histogram-bin-count=""
                                loext:histogram-overflow-bin=""
                                loext:histogram-underflow-bin=""
                                loext:histogram-interval-closed="true"/>

If an attribute does not exist, you simple omit the attribute. 
(Precondition it is set as 'optional' in the schema, as it is in your 
case.) So the element would be
<loext:histogram-configuration loext:histogram-frequency-type="0"
                                loext:histogram-interval-closed="true"/>

Kind regards,
Regina