Fix passing missing context to expression of select by expression algorithm

Author: signedav

python/plugins/processing/algs/qgis/SelectByExpression.py

@@ -87,6 +87,8 @@ def processAlgorithm(self, parameters, context, feedback):
         if qExp.hasParserError():
             raise QgsProcessingException(qExp.parserErrorString())
 
-        layer.selectByExpression(expression, behavior)
+        expression_context = self.createExpressionContext(parameters, context)
+
+        layer.selectByExpression(expression, behavior, expression_context)
 
         return {self.OUTPUT: parameters[self.INPUT]}