Skip printing error if empty for reporting bandwidth

[kerneltime]

Description

Skip printing error field when empty. This is used by mc to report bandwidth.

Motivation and Context

How to test this PR?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Documentation updated
• Unit tests added/updated

[minio-trusted]

Mint Automation

Test	Result
mint-large-bucket.sh	✔️
mint-fs.sh	✔️
mint-gateway-s3.sh	✔️
mint-erasure.sh	✔️
mint-dist-erasure.sh	✔️
mint-zoned.sh	✔️
mint-gateway-nas.sh	✔️
mint-compress-encrypt-dist-erasure.sh	❌ more...

11606-9d14971/mint-compress-encrypt-dist-erasure.sh.log:

Running with
SERVER_ENDPOINT:      minio-dev6.minio.io:30514
ACCESS_KEY:           minio
SECRET_KEY:           ***REDACTED***
ENABLE_HTTPS:         0
SERVER_REGION:        us-east-1
MINT_DATA_DIR:        /mint/data
MINT_MODE:            full
ENABLE_VIRTUAL_STYLE: 0

To get logs, run 'docker cp 894c31f176f2:/mint/log /tmp/mint-logs'

(1/15) Running aws-sdk-go tests ... done in 2 seconds
(2/15) Running aws-sdk-java tests ... done in 2 seconds
(3/15) Running aws-sdk-php tests ... done in 43 seconds
(4/15) Running aws-sdk-ruby tests ... done in 4 seconds
(5/15) Running awscli tests ... FAILED in 33 seconds
{
  "name": "awscli",
  "duration": 2625,
  "function": "aws --endpoint-url http://minio-dev6.minio.io:30514 s3api copy-object --bucket awscli-mint-test-bucket-4322 --key datafile-1-kB-copy --copy-source awscli-mint-test-bucket-4322/datafile-1-kB\n",
  "status": "FAIL",
  "error": "Hash mismatch expected 084e1383b70fb0c51acc680fef370023, got ac57de7156d7fc25ac1a65f81fa3989b"
}
(5/15) Running healthcheck tests ... done in 0 seconds
(6/15) Running mc tests ... done in 52 seconds
(7/15) Running minio-dotnet tests ... done in 58 seconds
(8/15) Running minio-go tests ... FAILED in 2 minutes and 28 seconds
{
  "args": {
    "destination": {
      "Bucket": "minio-go-test-5ukajoch14d9qthi",
      "Object": "dstObject",
      "Encryption": {},
      "UserMetadata": null,
      "ReplaceMetadata": false,
      "UserTags": null,
      "ReplaceTags": false,
      "LegalHold": "",
      "Mode": "",
      "RetainUntilDate": "0001-01-01T00:00:00Z",
      "Size": 0,
      "Progress": null
    },
    "source": {
      "Bucket": "minio-go-test-5ukajoch14d9qthi",
      "Object": "srcObject",
      "VersionID": "",
      "MatchETag": "",
      "NoMatchETag": "",
      "MatchModifiedSince": "0001-01-01T00:00:00Z",
      "MatchUnmodifiedSince": "0001-01-01T00:00:00Z",
      "MatchRange": false,
      "Start": 0,
      "End": 0,
      "Encryption": null
    }
  },
  "duration": 4905,
  "error": "We encountered an internal error, please try again.: cause(s2: corrupt input)",
  "function": "CopyObject(destination, source)",
  "message": "GetObject failed",
  "name": "minio-go: testUnencryptedToSSES3CopyObject",
  "status": "FAIL"
}
(8/15) Running minio-java tests ... FAILED in 1 minutes and 44 seconds
{
  "name": "minio-java",
  "function": "copyObject()",
  "args": "[match etag]",
  "duration": 207,
  "status": "FAIL",
  "error": "error occurred\nErrorResponse(code = PreconditionFailed, message = At least one of the pre-conditions you specified did not hold, bucketName = minio-java-test-1prs1le, objectName = minio-java-test-2dsnsq4-copy, resource = /minio-java-test-1prs1le/minio-java-test-2dsnsq4-copy, requestId = 166623502C95CE50, hostId = cbc8bf0d-038c-4376-8791-d81c050cdf85)\nrequest={method=PUT, url=http://minio-dev6.minio.io:30514/minio-java-test-1prs1le/minio-java-test-2dsnsq4-copy, headers=x-amz-copy-source-if-match: 71cff0a060f852067e443ad1e24ae26c-1\nx-amz-copy-source: /minio-java-test-1g55br5/minio-java-test-2dsnsq4\nHost: minio-dev6.minio.io:30514\nAccept-Encoding: identity\nUser-Agent: MinIO (Linux; amd64) minio-java/8.0.3\nContent-MD5: 1B2M2Y8AsgTpgAmY7PhCfg==\nx-amz-content-sha256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855\nx-amz-date: 20210222T175223Z\nAuthorization: AWS4-HMAC-SHA256 Credential=*REDACTED*/20210222/us-east-1/s3/aws4_request, SignedHeaders=content-md5;host;x-amz-content-sha256;x-amz-copy-source;x-amz-copy-source-if-match;x-amz-date, Signature=*REDACTED*\n}\nresponse={code=412, headers=Accept-Ranges: bytes\nContent-Length: 418\nContent-Security-Policy: block-all-mixed-content\nContent-Type: application/xml\nETag: \"71cff0a060f852067e443ad1e24ae26c\"\nLast-Modified: Mon, 22 Feb 2021 17:52:23 GMT\nServer: MinIO\nVary: Origin\nX-Amz-Request-Id: 166623502C95CE50\nX-Xss-Protection: 1; mode=block\nDate: Mon, 22 Feb 2021 17:52:23 GMT\n}\n >>> [io.minio.MinioClient.execute(MinioClient.java:775), io.minio.MinioClient.execute(MinioClient.java:563), io.minio.MinioClient.executePut(MinioClient.java:904), io.minio.MinioClient.copyObject(MinioClient.java:1232), FunctionalTest.testCopyObjectMatchETag(FunctionalTest.java:1850), FunctionalTest.copyObject(FunctionalTest.java:2016), FunctionalTest.runObjectTests(FunctionalTest.java:3757), FunctionalTest.runTests(FunctionalTest.java:3783), FunctionalTest.main(FunctionalTest.java:3927)]"
}
(8/15) Running minio-js tests ... done in 52 seconds
(9/15) Running minio-py tests ... done in 3 minutes and 6 seconds
(10/15) Running s3cmd tests ... FAILED in 6 seconds
{
  "name": "s3cmd",
  "duration": "3097",
  "function": "test_put_object_multipart",
  "status": "FAIL",
  "error": "WARNING: MD5 Sums don't match!\nWARNING: Retrying upload of /mint/data/datafile-65-MB\nWARNING: MD5 Sums don't match!\nWARNING: Retrying upload of /mint/data/datafile-65-MB\nWARNING: MD5 Sums don't match!\nWARNING: Retrying upload of /mint/data/datafile-65-MB\nWARNING: MD5 Sums don't match!\nWARNING: Retrying upload of /mint/data/datafile-65-MB\nWARNING: MD5 Sums don't match!\nWARNING: Retrying upload of /mint/data/datafile-65-MB\nWARNING: MD5 Sums don't match!\nWARNING: Too many failures. Giving up on '/mint/data/datafile-65-MB'\nERROR: \nUpload of '/mint/data/datafile-65-MB' part 1 failed. Use\n  /usr/local/bin/s3cmd abortmp s3://s3cmd-test-bucket-22815/s3cmd-test-object-29944 b1ad98bf-0d87-4e60-ad9b-6894b3f555f3\nto abort the upload, or\n  /usr/local/bin/s3cmd --upload-id b1ad98bf-0d87-4e60-ad9b-6894b3f555f3 put ...\nto continue the upload.\nERROR: Upload of '/mint/data/datafile-65-MB' failed too many times (Last reason: )"
}
(10/15) Running s3select tests ... done in 8 seconds
(11/15) Running security tests ... done in 0 seconds

Executed 11 out of 15 tests successfully.

Deleting image on docker hub
Deleting image locally