Modify the "toModify" argument in consideration of the "toConsider"
argument. Return the resulting Map, which may or may not be the same
reference as the "toModify" argument.
The modification performed is implementation-specific -- implementations
of this interface exist to perform some particular transformation on
the toModify argument given the toConsider argument.
Parameters: toModify - - modify this map Parameters: toConsider - - in consideration of this map the modified Map throws: IllegalArgumentException - if either toModify or toConsider is null