release-20.1: sql: fix panic when showing histograms on all-null columns #56515
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Backport 1/1 commits from #56434.
/cc @cockroachdb/release
Prior to this commit, attempting to view statistics for a column in which
all values were null could cause the system to panic. This was because the
histogram data was empty, and we were trying to decode an empty byte string.
This commit fixes the panic by checking if the byte string is empty before
trying to decode it, and also ensuring that the column type for the histogram
is set even if there are no buckets.
Fixes #56356
Release note (bug fix): Fixed a panic that could occur when running
SHOW STATISTICS USING JSON
for a table in which at least one of the columnscontained all null values.