Panic from cluster.check

[Jackbennett]

Describe the bug
cluster.check from weed shell errors with a stack trace.

System Setup

• command weed -v 4 -config_dir ./config/ shell
• OS version VERSION="18.04.3 LTS (Bionic Beaver)"
• output of weed version version 30GB 2.98 c6ec5269f4b34d79ab8e13050623501b8befda32 linux amd64
• scaffold of filer.toml in use.

[leveldb2]
# local on disk, mostly for simple single-machine setup, fairly scalable
# faster than previous leveldb, recommended.
enabled = true
dir = "./filerldb2"                    # directory to store level db files

> /srv/seaweedfs/production$ weed -v 4 -config_dir ./config/ shell
I0412 10:21:03 21181 config.go:59] Reading security.toml from /srv/seaweedfs/production/config/security.toml
I0412 10:21:03 21181 config.go:46] Reading : Config File "shell" Not Found in "[/srv/seaweedfs/production/config /srv/seaweedfs/production /home/jackben/.seaweedfs /usr/local/etc/seaweedfs /etc/seaweedfs]"
I0412 10:21:03 21181 masterclient.go:56] adminShell masterClient bootstraps with masters map[localhost:9333:localhost:9333]
I0412 10:21:03 21181 masterclient.go:104] adminShell masterClient Connecting to master localhost:9333
I0412 10:21:03 21181 masterclient.go:127] adminShell masterClient Connected to localhost:9333
master: localhost:9333 filers: [10.9.8.21:8888]
> cluster.check
Topology volumeSizeLimit:2048 MB hdd(volume:0/399 active:0 free:399 remote:0)
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x1d88008]

goroutine 1 [running]:
github.com/chrislusf/seaweedfs/weed/shell.(*commandClusterCheck).Do(0xc000175cc0?, {0x42e97c8, 0x0, 0x0}, 0xc0007343c0, {0x2e062a0, 0xc00013a008})
	/github/workspace/weed/shell/command_cluster_check.go:51 +0x248
github.com/chrislusf/seaweedfs/weed/shell.processEachCmd(0xc00053ffe0?, {0xc00053ffe0, 0xd}, 0x1?)
	/github/workspace/weed/shell/shell_liner.go:136 +0x3a7
github.com/chrislusf/seaweedfs/weed/shell.RunShell({0xc000532490, {0x2e04600, 0xc00000e1f8}, {0x0, 0x0}, 0x0, {0x0, 0x0}, {0x27da260, 0x1}})
	/github/workspace/weed/shell/shell_liner.go:105 +0x525
github.com/chrislusf/seaweedfs/weed/command.runShell(0x4295358?, {0xc0001181d0?, 0x0?, 0x0?})
	/github/workspace/weed/command/shell.go:59 +0x2d8
main.main()
	/github/workspace/weed/weed.go:81 +0x383

Additional context
Really trying to filer.sync from an initial weed server test setup, but err from weed -config_dir ./config/ filer.sync -isActivePassive -a localhost:9999 -b localhost:8888 results in E0412 10:37:07 25622 filer_sync.go:105] sync from localhost:9999 to localhost:8888: GetFilerConfiguration localhost:9999: rpc error: code = Unavailable desc = connection error: desc = "transport: authentication handshake failed: tls: first record does not look like a TLS handshake" so I'm checking the cluster is OK before getting into that error.

Also, this the security.toml note redactedN are all different hashes. If they/some need to be the same that's not in documentation I found.

# Put this file to one of the location, with descending priority
#    ./security.toml
#    $HOME/.seaweedfs/security.toml
#    /etc/seaweedfs/security.toml
# this file is read by master, volume server, and filer

# this jwt signing key is read by master and volume server, and it is used for write operations:
# - the Master server generates the JWT, which can be used to write a certain file on a volume server
# - the Volume server validates the JWT on writing
# the jwt defaults to expire after 10 seconds.
[jwt.signing]
key = "redacted1"
expires_after_seconds = 10           # seconds

# by default, if the signing key above is set, the Volume UI over HTTP is disabled.
# by setting ui.access to true, you can re-enable the Volume UI. Despite
# some information leakage (as the UI is not authenticated), this should not
# pose a security risk.
[access]
ui = true

# this jwt signing key is read by master and volume server, and it is used for read operations:
# - the Master server generates the JWT, which can be used to read a certain file on a volume server
# - the Volume server validates the JWT on reading
# NOTE: jwt for read is only supported with master+volume setup. Filer does not support this mode.
[jwt.signing.read]
key = "redacted2"
expires_after_seconds = 10           # seconds


# If this JWT key is configured, Filer only accepts writes over HTTP if they are signed with this JWT:
# - f.e. the S3 API Shim generates the JWT
# - the Filer server validates the JWT on writing
# the jwt defaults to expire after 10 seconds.
[jwt.filer_signing]
key = "redacted3"
expires_after_seconds = 10           # seconds

# If this JWT key is configured, Filer only accepts reads over HTTP if they are signed with this JWT:
# - f.e. the S3 API Shim generates the JWT
# - the Filer server validates the JWT on writing
# the jwt defaults to expire after 10 seconds.
[jwt.filer_signing.read]
key = "redacted4"
expires_after_seconds = 10           # seconds

# all grpc tls authentications are mutual
# the values for the following ca, cert, and key are paths to the PERM files.
# the host name is not checked, so the PERM files can be shared.
[grpc]
ca = "/srv/seaweedfs/production/CertificateAuthority/out/SeaweedFS_CA.crt"
# Set wildcard domain for enable TLS authentication by common names
allowed_wildcard_domain = "" # .mycompany.com

[grpc.volume]
cert = "/srv/seaweedfs/production/CertificateAuthority/out/volume01.crt"
key = "/srv/seaweedfs/production/CertificateAuthority/out/volume01.key"
allowed_commonNames = ""    # comma-separated SSL certificate common names

[grpc.master]
cert = "/srv/seaweedfs/production/CertificateAuthority/out/master01.crt"
key = "/srv/seaweedfs/production/CertificateAuthority/out/master01.key"
allowed_commonNames = ""    # comma-separated SSL certificate common names

[grpc.filer]
cert = "/srv/seaweedfs/production/CertificateAuthority/out/filer01.crt"
key = "/srv/seaweedfs/production/CertificateAuthority/out/filer01.key"
allowed_commonNames = ""    # comma-separated SSL certificate common names

[grpc.msg_broker]
cert = ""
key = ""
allowed_commonNames = ""    # comma-separated SSL certificate common names

# use this for any place needs a grpc client
# i.e., "weed backup|benchmark|filer.copy|filer.replicate|mount|s3|upload"
[grpc.client]
cert = "/srv/seaweedfs/production/CertificateAuthority/out/client01.crt"
key = "/srv/seaweedfs/production/CertificateAuthority/out/client01.key"

# volume server https options
# Note: work in progress!
#     this does not work with other clients, e.g., "weed filer|mount" etc, yet.
[https.client]
enabled = true

[https.volume]
cert = ""
key = ""
ca = ""

[https.master]
cert = ""
key = ""
ca = ""

[chrislusf]

Thanks for the detailed report!