add default value {} for 'ground_motion_correlation_params' ini parameter
add default value {} for 'ground_motion_correlation_params' ini parameter


Former-commit-id: 0208e15f5a2bdcd303e7cf0e631672244923da7d [formerly ccfb92be34c6d0cc3b43d8ad108261a25395f493] [formerly ccfb92be34c6d0cc3b43d8ad108261a25395f493 [formerly ccece48f17b8c69231b9797d219c89b9c7f3d2d1]]
Former-commit-id: 79330e569de6cb36deb64939be4d6b4da3d41c0a
Former-commit-id: f824e0a7b48f5ab2511556380183e7ab6ac93857
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine