add some null case handling

Author: cen1

core/src/main/java/com/kumuluz/ee/rest/beans/QueryParameters.java

@@ -115,6 +115,17 @@ public void addFilter(QueryFilter filter) {
         }
     }
 
+    /**
+     * Removes all filter parameters with the specified field name.
+     *
+     * @param field the field name of the filters to remove
+     */
+    public void removeFilterParameter(String field) {
+        if (field != null && filters != null) {
+            filters.removeIf(filter -> field.equals(filter.getField()));
+        }
+    }
+
     /**
      * @deprecated Will be removed in future releases. Use {@link #setFilterExpression(QueryFilterExpression)} ()}
      * instead.
@@ -145,6 +156,19 @@ public QueryFilterExpression getFilterExpression() {
         return filterExpression;
     }
 
+    /**
+     * Safely returns all filter values from the filter expression.
+     * Returns an empty list if filterExpression is null.
+     *
+     * @return list of QueryFilter values, never null
+     */
+    public List<QueryFilter> getFilterValues() {
+        if (filterExpression == null) {
+            return new ArrayList<>();
+        }
+        return filterExpression.getAllValues();
+    }
+
     public void setFilterExpression(QueryFilterExpression filterExpression) {
         this.filterExpression = filterExpression;
     }

core/src/main/java/com/kumuluz/ee/rest/utils/JPAUtils.java

@@ -555,6 +555,10 @@ private static CriteriaWhereQuery createWhereQueryInternal(EntityManager em, Cri
 
     private static Predicate createWhereQueryInternal(EntityManager em, CriteriaBuilder cb, Root<?> r, AtomicBoolean containsToManyAtomic, QueryFilterExpression filterExpression, Map<String, From> fieldJoins) {
 
+        if (filterExpression == null) {
+            return null;
+        }
+
         if (filterExpression.isLeaf()) {
             QueryFilter f = filterExpression.value();
 

core/src/main/java/com/kumuluz/ee/rest/utils/QueryStringBuilder.java

@@ -497,6 +497,11 @@ private List<String> buildFields(String value) {
     private QueryFilterExpression buildFilterExpression(String key, String value) {
         log.finest("Building filter string: " + value);
 
+        // Skip filters with empty values (e.g., "field:like:" with no value after operator)
+        if (value == null || value.isEmpty() || value.matches(".*:\\s*$")) {
+            return null;
+        }
+
         QueryFilterExpressionParser parser = Parboiled.createParser(QueryFilterExpressionParser.class, key);
 
         QueryFilterExpression filterExpression;