Fixed an issue with the dialect's _get_join_whereclause method, where it was causing a dangling "AND" to show up in the resultant query.

sqlbase7_sa/base.py

@@ -41,7 +41,7 @@ class SQLBase7Compiler(SQLCompiler):
     def visit_select(self, select, **kwargs):
         froms = select._get_display_froms()
         whereclause = self._get_join_whereclause(froms)
-        if whereclause is not None:
+        if whereclause:
             select = select.where(whereclause)
 
         kwargs['iswrapper'] = getattr(select, '_is_wrapper', False)
@@ -60,7 +60,9 @@ class SQLBase7Compiler(SQLCompiler):
             if isinstance(f, Join):
                 visit_join(f)
 
+        if clauses:
             return and_(*clauses)
+        return None
 
     def visit_ilike_op(self, binary, **kw):
         escape = binary.modifiers.get("escape", None)