How PHP recursively converts null in an array to an empty string "method

In some interface calls, directly querying the database out of the field may be a null field, but for the sake of a simple front-end judgment, you need to convert null to an empty string ', this time it needs to be recursive way. The direct code is as follows:


//recursively converts an array or string NULL to a null ' string     Public function_unsetnull ($arr){        if($arr!==NULL){            if(Is_array($arr)){                if(!Empty($arr)){                    foreach($arr  as $key=$value){                        if($value===NULL){                            $arr[$key] = "; }Else{                            $arr[$key] =$this->_unsetnull ($value);//recursion to execute again                        }                    }                }Else{$arr= ' '; } }Else{                if($arr===NULL){$arr= "; }//note three equals sign            }        }Else{$arr= ' '; } return $arr; }

How PHP recursively converts null in an array to an empty string "method