Part 2: add an EmptyBecause case for fulltext/non-string type mismatch.

query-algebrizer/src/cc.rs

@@ -173,6 +173,9 @@ impl Debug for EmptyBecause {
             &NonNumericArgument => {
                 write!(f, "Non-numeric argument in numeric place")
             },
+            &NonStringFulltextValue => {
+                write!(f, "Non-string argument for fulltext attribute")
+            },
             &UnresolvedIdent(ref kw) => {
                 write!(f, "Couldn't resolve keyword {}", kw)
             },

query-algebrizer/src/types.rs

@@ -297,11 +297,12 @@ impl Debug for ColumnConstraint {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Clone)]
 pub enum EmptyBecause {
     // Var, existing, desired.
     TypeMismatch(Variable, HashSet<ValueType>, ValueType),
     NonNumericArgument,
+    NonStringFulltextValue,
     UnresolvedIdent(NamespacedKeyword),
     InvalidAttributeIdent(NamespacedKeyword),
     InvalidAttributeEntid(Entid),