Try this:

if docs:
    return {
'doc_ids': data['ids'],
'doc_model': data['model'],
'date_start': date_start,
'date_end': date_end,
 'docs': docs,
    }
else:
    raise UserError(_("""No Data\n""") )
 

Hello Rishan,

You can do like below.

i n  render_html you can raise error message, if you set you report names like below

class YourModuleName (models.AbstractModel):

_ name = 'report.module_name.template_name'

@ api.multi
def render_html (self, docids, data = None):
    report_obj = self.env ['report']
    raise UserError (_ ('Example Error Message!')) 
    report = report_obj._get_report_from_name ('modulename.template_name' ) 
    docargs = {} 
    docargs.update ({
        'doc_ids': docids,
        'doc_model': 'mrp.production',
        'docs': mrp,
})
return report_obj.render ('modulename.template_name', docargs)

in report view

<report> .....

file = "modulename.template_name" 
name = "modulename.template_name"

and..

<template  ​id  ="template_name">

Please try like this if not worked, Please ask me.