Equality ($eq) was previously omitted from the queryOperatorMap because it is was used as the default return value for the MatchExpressionParser::parsePathAcceptingKeyword method when an operator was not recognized. Since then MatchExpressionParser::parsePathAcceptingKeyword has been modified to return a boost::optional and we can now differentiate.

As part of this work we should also remove the TODO for SERVER-19565 which called out the above omission.