Add explicit EOF and use assert instead of exception (#11041)

core/src/main/antlr4/org/apache/druid/math/expr/antlr/Expr.g4

@@ -15,6 +15,8 @@
 
 grammar Expr;
 
+start : expr EOF;
+
 expr : NULL                                                         # null
      | ('-'|'!') expr                                               # unaryOpExpr
      |<assoc=right> expr '^' expr                                   # powOpExpr

sql/src/main/java/org/apache/druid/sql/calcite/filtration/BottomUpTransform.java

@@ -36,7 +36,8 @@ public abstract class BottomUpTransform implements Function<Filtration, Filtrati
   private DimFilter checkedProcess(final DimFilter filter)
   {
     final DimFilter retVal = process(Preconditions.checkNotNull(filter, "filter"));
-    return Preconditions.checkNotNull(retVal, "process(filter) result in %s", getClass().getSimpleName());
+    assert retVal != null;
+    return retVal;
   }
 
   @Override