Fix couple of issues

[pawanrawal]

Fixes #1477 and #1464.

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This change is 

[manishrjain]

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Reviewed 4 of 4 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[janardhan1993]

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Reviewed 4 of 4 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion, some commit checks pending.

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client/client.go, line 298 at r1 (raw file):

	if len(val) == 0 {
		val = "_nil_"

Have similar checks at server side also, incase if we support grpc clients in other languages also.

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Comments from Reviewable

[pawanrawal]

Merged to master.