fix: address compatibility issues in table() with fully-qualified t…

…able names (#153)

* fix: address compatibility issues in `table()` with fully-qualified table names

* fix mypy

ibis_bigquery/__init__.py

@@ -188,11 +188,12 @@ def table(self, name, database=None) -> ir.TableExpr:
         return rename_partitioned_column(t, bq_table, self.partition_column)
 
     def _fully_qualified_name(self, name, database):
-        default_project, default_dataset = self._parse_project_and_dataset(database)
         parts = name.split(".")
         if len(parts) == 3:
             return name
-        elif len(parts) == 2:
+
+        default_project, default_dataset = self._parse_project_and_dataset(database)
+        if len(parts) == 2:
             return "{}.{}".format(default_project, name)
         elif len(parts) == 1:
             return "{}.{}.{}".format(default_project, default_dataset, name)
@@ -324,7 +325,7 @@ def exists_database(self, name):
         else:
             return True
 
-    def exists_table(self, name: str, database: str = None) -> bool:
+    def exists_table(self, name: str, database: Optional[str] = None) -> bool:
         """
         Return whether a table name exists in the database.