feat(core/webdaql): add is not null syntax

packages/core/src/stores/webdaql/WebdaQLParser.g4

@@ -17,6 +17,9 @@ expression
     identifier LIKE stringLiteral #likeExpression
     | identifier IN setExpression #inExpression
     | identifier CONTAINS stringLiteral #containsExpression
+    // IS NULL / IS NOT NULL
+    | identifier IS NULL #isNullExpression
+    | identifier IS NOT NULL #isNotNullExpression
     // Comparison operations
     | identifier (EQUAL | NOT_EQUAL | GREATER_OR_EQUAL | LESS_OR_EQUAL | LESS | GREATER) values #binaryComparisonExpression
     // Logic operations

packages/core/src/stores/webdaql/query.ts

@@ -233,6 +233,22 @@
       return new ComparisonExpression("CONTAINS", left.text, value);
     }
 
+    /**
+     * IS NULL expression
+     */
+    visitIsNullExpression(ctx: any) {
+      const left = ctx.getChild(0);
+      return new ComparisonExpression("IS NULL", left.text, null);
+    }
+
+    /**
+     * IS NOT NULL expression
+     */
+    visitIsNotNullExpression(ctx: any) {
+      const left = ctx.getChild(0);
+      return new ComparisonExpression("IS NOT NULL", left.text, null);
+    }
+
     /**
      * Get the OrExpression, regrouping all the parameters
      *
@@ -319,7 +335,7 @@
     abstract toString(depth?: number): string;
   }
 
-  export type ComparisonOperator = "=" | "<=" | ">=" | "<" | ">" | "!=" | "LIKE" | "IN" | "CONTAINS";
+  export type ComparisonOperator = "=" | "<=" | ">=" | "<" | ">" | "!=" | "LIKE" | "IN" | "CONTAINS" | "IS NULL" | "IS NOT NULL";
   /**
    * Comparison expression
    */
@@ -430,6 +446,10 @@
             return left.includes(this.value);
           }
           return false;
+        case "IS NOT NULL":
+          return left !== null && left !== undefined;
+        case "IS NULL":
+          return left === null || left === undefined;
       }
     }