quick fix: add eq/ne filter format for null

Somewhat incomplete fix, proper fix would require a lot of rewrite.

issue: gql cannot search for property != bool, because null bool values exist in the pod

example:

Filter i want to write is

filter {isMock: {ne: 1}}

Results in SQL:

WHERE isMock != 1

This fails, because we're comparing to NULL.

Quick fix, rewrite the query to search for isMock = 0 OR isMock is NULL. However:

query {
  Message (filter: isMock: {eq: null}}) {
    isMock
  }
}

gets converted to sql:

...
WHERE isMock = null

Also fails, we want to search for is NULL

This fix changes = to is in sql query if null filter value. Now to actually search for isMock != 1:

query {
  Message (filter: {or: [{isMock: {eq: null}}, {isMock: {eq: 0}}]}) {
    isMock
  }
}