[CALCITE-6105] Documentation does not specify the behavior of SPLIT f…

…unction for empty string arguments

Signed-off-by: Mihai Budiu <[email protected]>

site/_docs/reference.md

@@ -2823,7 +2823,7 @@ BigQuery's type system uses confusingly different names for types and functions:
 | b m o p | SOUNDEX(string)                          | Returns the phonetic representation of *string*; throws if *string* is encoded with multi-byte encoding such as UTF-8
 | s | SOUNDEX(string)                                | Returns the phonetic representation of *string*; return original *string* if *string* is encoded with multi-byte encoding such as UTF-8
 | m | SPACE(integer)                                 | Returns a string of *integer* spaces; returns an empty string if *integer* is less than 1
-| b | SPLIT(string [, delimiter ])                   | Returns the string array of *string* split at *delimiter* (if omitted, default is comma)
+| b | SPLIT(string [, delimiter ])                   | Returns the string array of *string* split at *delimiter* (if omitted, default is comma).  If the *string* is empty it returns an empty array, otherwise, if the *delimiter* is empty, it returns an array containing the original *string*.
 | b | STARTS_WITH(string1, string2)                  | Returns whether *string2* is a prefix of *string1*
 | m | STRCMP(string, string)                         | Returns 0 if both of the strings are same and returns -1 when the first argument is smaller than the second and 1 when the second one is smaller than the first one
 | b p | STRPOS(string, substring)                    | Equivalent to `POSITION(substring IN string)`