Do nothing if em.insertMany() is passed an empty array

[squivix]

Is your feature request related to a problem? Please describe.
When calling em.insertMany() with an empty array instead of doing nothing it tries to insert anyway and generates an invalid query, resulting in:

insert into "entity" ("id") values  returning "id" - syntax error at or near "returning"

Describe the solution you'd like
I want it to ignore an empty array of entities. I know it's supposed to be a native insert query that provides direct access to the db, but I think this simple convenience like this is not too much to ask.

Describe alternatives you've considered
I can always wrap my call in a check. For example:

const entityAs = await this.em.find(EntityA, filters);
if (entityAs.length > 0)
    await this.em.insertMany(PivotEntityAEntityB, entityAs.map(entityA => ({entityA, entityB: entityB})));

but it's wordy

Additional context
The invalid SQL query mentioned earlier is encountered in miko-orm 5.6.7.

Meanwhile in 6.0.0-dev.87 I seem to get a TypeError instead:

TypeError: Cannot use 'in' operator to search for 'id' in undefined
     at /home/user/WebstormProjects/project/node_modules/@mikro-orm/knex/AbstractSqlDriver.js:318:45
     at Array.filter (<anonymous>)
     at PostgreSqlDriver.nativeInsertMany (/home/user/WebstormProjects/project/node_modules/@mikro-orm/knex/AbstractSqlDriver.js:318:18)
     at SqlEntityManager.insertMany (/home/user/WebstormProjects/project/node_modules/@mikro-orm/core/EntityManager.js:850:37)

[rubiin]

@B4nan

mikro-orm/packages/core/src/EntityManager.ts

Line 998 in f99298d

if (data === undefined) {

I think we can also add a length check for data in here