[query] add specialized matchers for empty EQ/NEQ matchers

[arnikola]

What this PR does / why we need it:
Fixes #1873

[robskillington]

LGTM

[codecov]

Codecov Report

Merging #1986 into master will increase coverage by 0.5%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #1986     +/-   ##
=========================================
+ Coverage      63%    63.6%   +0.5%     
=========================================
  Files        1123     1122      -1     
  Lines      106854   106597    -257     
=========================================
+ Hits        67419    67812    +393     
+ Misses      35061    34450    -611     
+ Partials     4374     4335     -39

Flag	Coverage Δ
#aggregator	79.7% <ø> (ø)	⬆️
#cluster	52.3% <ø> (-4%)	⬇️
#collector	57.9% <ø> (-5.9%)	⬇️
#dbnode	64.6% <ø> (+0.6%)	⬆️
#m3em	59.6% <ø> (ø)	⬆️
#m3ninx	27.4% <ø> (-33.5%)	⬇️
#m3nsch	41.4% <ø> (-9.8%)	⬇️
#metrics	53% <ø> (+35.2%)	⬆️
#msg	74% <ø> (-0.8%)	⬇️
#query	63.4% <100%> (-4.8%)	⬇️
#x	39.5% <ø> (-35.5%)	⬇️

---

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[arnikola]

github please

[codecov]

Codecov Report

Merging #1986 into master will decrease coverage by <.1%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #1986     +/-   ##
=========================================
- Coverage    63.6%    63.6%   -0.1%     
=========================================
  Files        1124     1122      -2     
  Lines      106753   106597    -156     
=========================================
- Hits        67917    67812    -105     
+ Misses      34488    34450     -38     
+ Partials     4348     4335     -13

Flag	Coverage Δ
#aggregator	79.7% <ø> (ø)	⬆️
#cluster	52.3% <ø> (-4.1%)	⬇️
#collector	57.9% <ø> (-5.9%)	⬇️
#dbnode	64.6% <ø> (-0.4%)	⬇️
#m3em	59.6% <ø> (ø)	⬆️
#m3ninx	27.4% <ø> (-33.7%)	⬇️
#m3nsch	41.4% <ø> (-9.8%)	⬇️
#metrics	53% <ø> (+35.2%)	⬆️
#msg	74% <ø> (-0.8%)	⬇️
#query	63.4% <100%> (-5.3%)	⬇️
#x	39.5% <ø> (-35.5%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1eb7e3f...383c4be. Read the comment docs.