Getting "Missing key name" when trying to view Key/Value index in the UI

#### Overview of the Issue

When clicking the "key/value" button on top [ `.../v1/kv/?keys&dc=dc1&separator=%2F` ], I am getting a 400 response with the response text being simply: "Missing key name". Any idea what can cause this?

#### Reproduction Steps

1. Go to consul UI
2. Click Key/Value

### Consul info for both Client and Server

Server info

```
agent:
check_monitors = 0
check_ttls = 0
checks = 0
services = 0
build:
prerelease =
revision = a9322b9c
version = 1.8.3
consul:
acl = disabled
bootstrap = true
known_datacenters = 1
leader = true
leader_addr = 10.0.0.18:8300
server = true
raft:
applied_index = 15514
commit_index = 15514
fsm_pending = 0
last_contact = 0
last_log_index = 15514
last_log_term = 6
last_snapshot_index = 0
last_snapshot_term = 0
latest_configuration = [{Suffrage:Voter ID:4e1ce8e9-b424-e3a2-f442-a67ebbd8e226 Address:10.0.0.18:8300}]
latest_configuration_index = 0
num_peers = 0
protocol_version = 3
protocol_version_max = 3
protocol_version_min = 0
snapshot_version_max = 1
snapshot_version_min = 0
state = Leader
term = 6
runtime:
arch = amd64
cpu_count = 1
goroutines = 101
max_procs = 1
os = linux
version = go1.14.7
serf_lan:
coordinate_resets = 0
encrypted = false
event_queue = 1
event_time = 6
failed = 0
health_score = 0
intent_queue = 0
left = 0
member_time = 1
members = 1
query_queue = 0
query_time = 1
serf_wan:
coordinate_resets = 0
encrypted = false
event_queue = 0
event_time = 1
failed = 0
health_score = 0
intent_queue = 0
left = 0
member_time = 1
members = 1
query_queue = 0
query_time = 1

```

### Operating system and Environment details

Ubuntu 20

Run command: `/usr/bin/consul agent -server -bootstrap-expect 1 -bind 0.0.0.0 -data-dir /opt/consul -config-dir=/etc/consul.d/ -ui`

Reproduce the issue by opening the Consul UI's Key/Value view and inspecting the /v1/kv/?keys&dc=dc1&separator=%2F request. Trace why this request returns 400 with "Missing key name"; done means the Key/Value index loads successfully without that error.

Written by the indexing model from the issue text.