Consider None values in TSQL conditions

Fixes #262

CHANGELOG.md

@@ -25,6 +25,8 @@ these changes are prefixed with "**BREAKING**"
   token, allowing for more informative syntax errors.
 * `delphin.tsql.select()` will raise a `TSQLError` if a condition's
   type does not match that of the column it checks ([#261][])
+* `delphin.tsql.select()` now considers ``None`` values when checking
+  conditions ([#262][])
 
 
 ## [v1.0.3][]
@@ -1216,5 +1218,6 @@ information about changes, except for
 [#253]: https://github.com/delph-in/pydelphin/issues/253
 [#257]: https://github.com/delph-in/pydelphin/issues/257
 [#261]: https://github.com/delph-in/pydelphin/issues/261
+[#262]: https://github.com/delph-in/pydelphin/issues/262
 [#263]: https://github.com/delph-in/pydelphin/issues/263
 [#264]: https://github.com/delph-in/pydelphin/issues/264

delphin/tsql.py

@@ -440,15 +440,15 @@ def func(row):
             index = field_index[body[0]]
             field = fields[index]
             value = tsdb.cast(field.datatype, row[index])
-            return re.search(body[1], value)
+            return value is not None and re.search(body[1], value)
 
     elif op == '!~':
 
         def func(row):
             index = field_index[body[0]]
             field = fields[index]
             value = tsdb.cast(field.datatype, row[index])
-            return not re.search(body[1], value)
+            return value is None or not re.search(body[1], value)
 
     else:
         compare = _operator_functions[op]
@@ -457,7 +457,7 @@ def func(row):
             index = field_index[body[0]]
             field = fields[index]
             value = tsdb.cast(field.datatype, row[index])
-            return compare(value, body[1])
+            return value is not None and compare(value, body[1])
 
     return func