Type error in CoEnrollmentFlowAuthzCouId

Browser(Chrome) halts on this line:

document.getElementById('CoEnrollmentFlowAuthzCouId').value = "";

with these errors:

Uncaught TypeError: Cannot set property 'value' of null

<exception>: TypeError
arguments: Array[2]
0: "value"
1: null
length: 2
_proto_: Array[0]
get message: function ()

{ [native code] }
arguments: null
caller: null
length: 0
name: ""
prototype: Object
_proto_: function Empty() {}
<function scope>
get stack: function () { [native code] }

set message: function ()

{ [native code] }
set stack: function () { [native code] }

type: "non_object_property_store"
_proto_: Error
authz: "A"
this: Window