Error in trickster log

[vuxuanlai]

Hi all,
I used trickster as proxy server for prometheus on k8s. I using helm chart to deploy trickster and value.yaml content as below:

origins:
  - name: default
    originType: prometheus
    originURL: http://prometheus-server.monitoring:8080
    timeoutSecs: "60"
    keepAliveTimeoutSecs: "180"
caches:
  - name: default
    cacheType: memory
    volumeName: trickster
    index:
      maxSizeBytes: "2147482548"
image:
  repository: tricksterproxy/trickster
  tag: "latest"
  pullPolicy: Always
volumes:
  generic:
    type: "generic"
    enabled: false
    mountPath: "/tmp/trickster"
resources:
  limits:
    cpu: 1000m
    memory: 1Gi
  requests:
    cpu: 100m
    memory: 128Mi

I got the error in Trickster log pod as the following:

time=2020-11-11T09:18:36.703819952Z app=trickster caller=proxy/engines/deltaproxycache.go:488 level=error event="unexpected upstream response" clientRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range clientRequestMethod=POST clientRequestHeaders="unsupported value type" upstreamRequestMethod=POST upstreamRequestHeaders="{[Content-Length:276],[Content-Type:application/x-www-form-urlencoded],[Forwarded:for=10.42.187.67;proto=http],[User-Agent:Go-http-client/1.1],[Via:HTTP/1.1 trickster-588c65fc47-qpqn2]}" statusCode=400 upstreamRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamResponseHeaders="{[Cache-Control:s-maxage=21600],[Content-Type:application/json],[Date:Wed, 11 Nov 2020 09:18:36 GMT]}" upstreamResponseBody="{\"status\":\"error\",\"errorType\":\"bad_data\",\"error\":\"1:135: parse error: missing unit character in duration\"}"
time=2020-11-11T09:18:36.708131332Z app=trickster caller=proxy/engines/deltaproxycache.go:488 level=error event="unexpected upstream response" statusCode=400 clientRequestMethod=POST upstreamRequestMethod=POST upstreamRequestHeaders="{[Content-Length:274],[Content-Type:application/x-www-form-urlencoded],[Forwarded:for=10.42.187.67;proto=http],[User-Agent:Go-http-client/1.1],[Via:HTTP/1.1 trickster-588c65fc47-qpqn2]}" clientRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range clientRequestHeaders="unsupported value type" upstreamRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamResponseHeaders="{[Cache-Control:s-maxage=21600],[Content-Type:application/json],[Date:Wed, 11 Nov 2020 09:18:36 GMT]}" upstreamResponseBody="{\"status\":\"error\",\"errorType\":\"bad_data\",\"error\":\"1:135: parse error: missing unit character in duration\"}"
time=2020-11-11T09:18:36.711124288Z app=trickster caller=proxy/engines/deltaproxycache.go:488 level=error event="unexpected upstream response" statusCode=400 clientRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range clientRequestMethod=POST clientRequestHeaders="unsupported value type" upstreamRequestHeaders="{[Content-Length:274],[Content-Type:application/x-www-form-urlencoded],[Forwarded:for=10.42.187.67;proto=http],[User-Agent:Go-http-client/1.1],[Via:HTTP/1.1 trickster-588c65fc47-qpqn2]}" upstreamResponseBody="{\"status\":\"error\",\"errorType\":\"bad_data\",\"error\":\"1:135: parse error: missing unit character in duration\"}" upstreamRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamRequestMethod=POST upstreamResponseHeaders="{[Cache-Control:s-maxage=21600],[Content-Type:application/json],[Date:Wed, 11 Nov 2020 09:18:36 GMT]}"
time=2020-11-11T09:19:12.787977014Z app=trickster caller=proxy/engines/deltaproxycache.go:488 level=error event="unexpected upstream response" clientRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range clientRequestMethod=POST upstreamRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamResponseHeaders="{[Cache-Control:s-maxage=21600],[Content-Type:application/json],[Date:Wed, 11 Nov 2020 09:19:12 GMT]}" upstreamResponseBody="{\"status\":\"error\",\"errorType\":\"bad_data\",\"error\":\"1:135: parse error: missing unit character in duration\"}" statusCode=400 upstreamRequestMethod=POST upstreamRequestHeaders="{[Content-Length:276],[Content-Type:application/x-www-form-urlencoded],[Forwarded:for=10.42.187.67;proto=http],[User-Agent:Go-http-client/1.1],[Via:HTTP/1.1 trickster-588c65fc47-qpqn2]}" clientRequestHeaders="unsupported value type"
time=2020-11-11T09:19:12.795047239Z app=trickster caller=proxy/engines/deltaproxycache.go:488 level=error event="unexpected upstream response" clientRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamRequestHeaders="{[Content-Length:274],[Content-Type:application/x-www-form-urlencoded],[Forwarded:for=10.42.187.67;proto=http],[User-Agent:Go-http-client/1.1],[Via:HTTP/1.1 trickster-588c65fc47-qpqn2]}" upstreamResponseHeaders="{[Cache-Control:s-maxage=21600],[Content-Type:application/json],[Date:Wed, 11 Nov 2020 09:19:12 GMT]}" upstreamResponseBody="{\"status\":\"error\",\"errorType\":\"bad_data\",\"error\":\"1:135: parse error: missing unit character in duration\"}" statusCode=400 clientRequestMethod=POST clientRequestHeaders="unsupported value type" upstreamRequestMethod=POST
time=2020-11-11T09:19:12.798483432Z app=trickster caller=proxy/engines/deltaproxycache.go:488 level=error event="unexpected upstream response" clientRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range clientRequestMethod=POST upstreamRequestURL=http://prometheus-server.monitoring:8080/api/v1/query_range upstreamResponseHeaders="{[Cache-Control:s-maxage=21600],[Content-Type:application/json],[Date:Wed, 11 Nov 2020 09:19:12 GMT]}" upstreamResponseBody="{\"status\":\"error\",\"errorType\":\"bad_data\",\"error\":\"1:135: parse error: missing unit character in duration\"}" statusCode=400 clientRequestHeaders="unsupported value type" upstreamRequestMethod=POST upstreamRequestHeaders="{[Content-Length:276],[Content-Type:application/x-www-form-urlencoded],[Forwarded:for=10.42.187.67;proto=http],[User-Agent:Go-http-client/1.1],[Via:HTTP/1.1 trickster-588c65fc47-qpqn2]}"

Could you please help me to explain this?
Thanks.