Running saveAsXML in a custom script tool and setting the input parameter with spaces in the file path in ArcGIS Pro returns an empty XML (extensible markup language).
There is an error in the custom script on line 90. Change the following line:
inMeta = arcpy.metadata.Metadata( item )
As illustrated here:
inMeta = arcpy.metadata.Metadata( item.replace("'", "") )
This change is required to remove single quotation marks from the path that is included in the path returned by the operating system when the item's name includes a space. To access the item's metadata, a path must be provided that does not include single quotation marks.
This same technique is used elsewhere in the same script to resolve the same problem when getting the feature class name from the path. However, the same technique needs to be applied on the above line as well to remove single quotation marks from the full path of the item that was provided via the input parameter in order to access the item's metadata.
The notes provided under the Additional Information heading prove that there is no problem using the SaveAsXML method when the input item's path includes spaces because it was noted that in other scenarios the script will generate FULL XML output 'even though the input is from a file path with space.'
The SaveAsXML method can't work with a space in one scenario and not work with a space in another scenario. Therefore, the problem has to be user error with the provided script