custom profile field: Don't push null values to json request.
custom profile field: Don't push null values to json request.

This commit add checks in frontend to remove null values of choices
from json data. This allows user to successfully create/edit choice
custom field, even if there is blank input in choices.

kou/zulip,jackrzhang/zulip,dhcrzf/zulip,kou/zulip,shubhamdhama/zulip,rht/zulip,zulip/zulip,brainwane/zulip,rishig/zulip,brainwane/zulip,synicalsyntax/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,dhcrzf/zulip,andersk/zulip,zulip/zulip,rishig/zulip,showell/zulip,kou/zulip,rishig/zulip,eeshangarg/zulip,shubhamdhama/zulip,timabbott/zulip,dhcrzf/zulip,dhcrzf/zulip,synicalsyntax/zulip,timabbott/zulip,eeshangarg/zulip,timabbott/zulip,timabbott/zulip,eeshangarg/zulip,tommyip/zulip,shubhamdhama/zulip,rht/zulip,jackrzhang/zulip,punchagan/zulip,synicalsyntax/zulip,kou/zulip,dhcrzf/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,timabbott/zulip,timabbott/zulip,eeshangarg/zulip,tommyip/zulip,rht/zulip,rishig/zulip,jackrzhang/zulip,andersk/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,shubhamdhama/zulip,tommyip/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,tommyip/zulip,jackrzhang/zulip,showell/zulip,shubhamdhama/zulip,rishig/zulip,hackerkid/zulip,dhcrzf/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,brainwane/zulip,jackrzhang/zulip,dhcrzf/zulip,shubhamdhama/zulip,synicalsyntax/zulip,tommyip/zulip,brainwane/zulip,synicalsyntax/zulip,showell/zulip,zulip/zulip,synicalsyntax/zulip,kou/zulip,rishig/zulip,zulip/zulip,punchagan/zulip,rishig/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,jackrzhang/zulip,kou/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,jackrzhang/zulip,tommyip/zulip,synicalsyntax/zulip,showell/zulip,shubhamdhama/zulip,eeshangarg/zulip,showell/zulip,showell/zulip,andersk/zulip,showell/zulip,brainwane/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,tommyip/zulip,hackerkid/zulip,rht/zulip,zulip/zulip