allow identifierQuoteString to be either empty ("") or null or both

[Allam76]

A jdbc driver can specify a identifier quote string with DatabaseMetaData.getIdentifierQuoteString.

My database does not allow quote strings but expects identifiers to be unquoted uppercase only. So I have the choise to set the quote string as either empty "" or null.

Sqlline allows an empty string in one part of the code:

sqlline/src/main/java/sqlline/DatabaseConnection.java

Line 75 in f7889ec

if (identifierQuoteString.length() > 1) {

and a null in another:

sqlline/src/main/java/sqlline/DialectImpl.java

Line 51 in f7889ec

if (identifierQuote == null) {

Please choose one or the other approach. Or maybe both :-) Many thanks.