This method is like _.merge except that it accepts customizer which
is invoked to produce the merged values of the destination and source
properties. If customizer returns undefined, merging is handled by
the method instead. The customizer is invoked with six arguments:
(objValue, srcValue, key, object, source, stack).
This method is like _.merge except that it accepts customizer which is invoked to produce the merged values of the destination and source properties. If customizer returns undefined, merging is handled by the method instead. The customizer is invoked with six arguments: (objValue, srcValue, key, object, source, stack).
Note: This method mutates object.