diff --git a/lib/sql.js b/lib/sql.js
index d9848ec..4fd0d11 100644
--- a/lib/sql.js
+++ b/lib/sql.js
@@ -754,9 +754,11 @@ SQLConnector.prototype._buildWhere = function(model, where) {
       if (Array.isArray(clauses)) {
         for (var i = 0, n = clauses.length; i < n; i++) {
           var stmtForClause = self._buildWhere(model, clauses[i]);
-          stmtForClause.sql = '(' + stmtForClause.sql + ')';
-          branchParams = branchParams.concat(stmtForClause.params);
-          branches.push(stmtForClause.sql);
+          if (stmtForClause.sql) {
+            stmtForClause.sql = '(' + stmtForClause.sql + ')';
+            branchParams = branchParams.concat(stmtForClause.params);
+            branches.push(stmtForClause.sql);
+          }
         }
         stmt.merge({
           sql: branches.join(' ' + key.toUpperCase() + ' '),
@@ -767,6 +769,12 @@ SQLConnector.prototype._buildWhere = function(model, where) {
       }
       // The value is not an array, fall back to regular fields
     }
+    var p = props[key];
+    if (p == null) {
+      // Unknown property, ignore it
+      debug('Unknown property %s is skipped for model %s', key, model);
+      continue;
+    }
     var columnName = self.columnEscaped(model, key);
     var expression = where[key];
     var columnValue;
@@ -782,10 +790,10 @@ SQLConnector.prototype._buildWhere = function(model, where) {
         if (Array.isArray(expression)) {
           // Column value is a list
           for (var j = 0, m = expression.length; j < m; j++) {
-            columnValue.push(this.toColumnValue(props[key], expression[j]));
+            columnValue.push(this.toColumnValue(p, expression[j]));
           }
         } else {
-          columnValue.push(this.toColumnValue(props[key], expression));
+          columnValue.push(this.toColumnValue(p, expression));
         }
         if (operator === 'between') {
           // BETWEEN v1 AND v2
@@ -807,14 +815,14 @@ SQLConnector.prototype._buildWhere = function(model, where) {
         // do not coerce RegExp based on property definitions
         columnValue = expression;
       } else {
-        columnValue = this.toColumnValue(props[key], expression);
+        columnValue = this.toColumnValue(p, expression);
       }
       sqlExp = self.buildExpression(
-        columnName, operator, columnValue, props[key]);
+        columnName, operator, columnValue, p);
       stmt.merge(sqlExp);
     } else {
       // The expression is the field value, not a condition
-      columnValue = self.toColumnValue(props[key], expression);
+      columnValue = self.toColumnValue(p, expression);
       if (columnValue === null) {
         stmt.merge(columnName + ' IS NULL');
       } else {