fix parsesql.treeRepr when nil is in input (#18974)

* fix parsesql.treeRepr when nil is in input

* return newNode(nkNone) as default value, not nil

tests/stdlib/tparsesql.nim

@@ -3,6 +3,17 @@ discard """
 """
 import parsesql
 
+doAssert treeRepr(parseSql("INSERT INTO STATS VALUES (10, 5.5); ")
+) == """
+
+nkStmtList
+  nkInsert
+    nkIdent STATS
+    nkNone
+    nkValueList
+      nkIntegerLit 10
+      nkNumericLit 5.5"""
+
 doAssert $parseSQL("SELECT foo FROM table;") == "select foo from table;"
 doAssert $parseSQL("""
 SELECT
@@ -183,8 +194,31 @@ SET ContactName = 'Alfred Schmidt', City= 'Frankfurt'
 WHERE CustomerID = 1;
 """) == "update Customers set ContactName  = 'Alfred Schmidt' , City  = 'Frankfurt' where CustomerID = 1;"
 
+doAssert treeRepr(parseSql("""UPDATE Customers
+                              SET ContactName = 'Alice', City= 'Frankfurt';""")
+) == """
+
+nkStmtList
+  nkUpdate
+    nkIdent Customers
+    nkAsgn
+      nkIdent ContactName
+      nkStringLit Alice
+    nkAsgn
+      nkIdent City
+      nkStringLit Frankfurt
+    nkNone"""
+
 doAssert $parseSQL("DELETE FROM table_name;") == "delete from table_name;"
 
+doAssert treeRepr(parseSQL("DELETE FROM table_name;")
+) == """
+
+nkStmtList
+  nkDelete
+    nkIdent table_name
+    nkNone"""
+
 doAssert $parseSQL("DELETE * FROM table_name;") == "delete from table_name;"
 
 doAssert $parseSQL("""