feat(cubesql): Parse NULL literal in LogicalPlanLanguage

Author: mcheshkov

rust/cubesql/cubesql/src/compile/rewrite/language.rs

@@ -644,6 +644,8 @@ macro_rules! variant_field_struct {
                     } else if let Some(value) = typed_str.strip_prefix("f:") {
                         let n: f64 = value.parse().map_err(|err| Self::Err::InvalidFloatValue(err))?;
                         Ok([<$variant $var_field:camel>](ScalarValue::Float64(Some(n))))
+                    } else if typed_str == "null" {
+                        Ok([<$variant $var_field:camel>](ScalarValue::Null))
                     } else {
                         Err(Self::Err::InvalidScalarType)
                     }

rust/cubesql/cubesql/src/compile/rewrite/mod.rs

@@ -1780,6 +1780,11 @@ fn literal_bool(literal_bool: bool) -> String {
     format!("(LiteralExpr LiteralExprValue:b:{})", literal_bool)
 }
 
+#[allow(dead_code)]
+fn literal_null() -> String {
+    format!("(LiteralExpr LiteralExprValue:null)")
+}
+
 fn projection(
     expr: impl Display,
     input: impl Display,