Projection/TPC issue: Query 7 - Matcherror for plain String pass-through

```
Query 7 *** FAILED ***
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Message:	input_4#1910 AS supp_nation#2064 (of class org.apache.spark.sql.catalyst.expressions.Alias)
Exception:	scala.MatchError
com.nec.spark.agile.SparkExpressionToCExpression$.evalString(SparkExpressionToCExpression.scala:161)
```