Http: proxy error: unsupported protocol scheme \"\

I have Installed latest Grafana 6.7.3 on a CENT OS machine. The DB I used is the default SQL-Lite. Most of the configuration is the default one. After installation while creating a dashboard and selcting metrics on the screen seeing “BAD Gateway” error. in the grafana logs I can see below error:
t=2020-05-13T12:51:25+0530 lvl=eror msg=“Data proxy error” logger=data-proxy-log userId=1 orgId=1 uname=admin path=/api/datasources/proxy/1/render remote_addr=<> referer=“http://:3000/dashboard/new?panelId=2&edit&fullscreen&orgId=1” error=“http: proxy error: unsupported protocol scheme “””
t=2020-05-13T12:51:25+0530 lvl=info msg=“Request Completed” logger=context userId=1 orgId=1 uname=admin method=POST path=/api/datasources/proxy/1/render status=502 remote_addr= time_ms=0 size=0 referer=“http://:3000/dashboard/new?panelId=2&edit&fullscreen&orgId=1”