There are a few Operations in Cascading (e.g., ExpressionFunction and ExpressionFilter) that compile and apply Java expressions on the fly. In these expressions, Operation argument field names are used as variable names in the expression. For this reason, take care to create field names that don't contain characters which will cause compilation errors if they are used in an expression. For example, "first-name" is a valid field name for use with Cascading, but might result in the expression first-name.trim(), which will cause a compilation error.