XGBoost panic

[Dig-Doug]

/home/doug/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/smartcore-0.4.9/src/xgboost/xgb_regressor.rs:315:34:                        
index out of bounds: the len is 0 but the index is 0                                                                                        
stack backtrace:                                                                                                                            
   0: __rustc::rust_begin_unwind                                                                                                            
   1: core::panicking::panic_fmt                                                                                                            
   2: core::panicking::panic_bounds_check                                                                                                   
   3: smartcore::xgboost::xgb_regressor::TreeRegressor<TX,TY,X,Y>::fit                                                                      
   4: smartcore::xgboost::xgb_regressor::TreeRegressor<TX,TY,X,Y>::fit                                                                      
   5: smartcore::xgboost::xgb_regressor::TreeRegressor<TX,TY,X,Y>::fit                                                                      
   6: smartcore::xgboost::xgb_regressor::TreeRegressor<TX,TY,X,Y>::fit                                                                      
   7: smartcore::xgboost::xgb_regressor::TreeRegressor<TX,TY,X,Y>::fit                                                                      
   8: smartcore::xgboost::xgb_regressor::TreeRegressor<TX,TY,X,Y>::fit                                                                      
   9: smartcore::xgboost::xgb_regressor::XGRegressor<TX,TY,X,Y>::fit