Let filter be ignored if they do not contain a filter value

cursorpaging-jpa/src/main/java/io/vigier/cursorpaging/jpa/Filter.java

@@ -2,13 +2,15 @@
 
 import jakarta.persistence.metamodel.SingularAttribute;
 import java.util.List;
+import java.util.Objects;
 import java.util.function.Consumer;
 import lombok.Builder;
 import lombok.EqualsAndHashCode;
 import lombok.Getter;
 import lombok.Singular;
 import lombok.With;
 import lombok.experimental.Accessors;
+import org.springframework.util.StringUtils;
 
 /**
  * A filter, which can be used to filter a query (remove elements from the result).
@@ -81,10 +83,17 @@ public static Filter attributeIs( final SingularAttribute<?, ? extends Comparabl
      * @param qb the query builder
      */
     public void apply( final QueryBuilder qb ) {
-        if ( values.size() > 1 ) {
-            qb.andWhere( qb.isIn( attribute, values ) );
-        } else {
-            qb.andWhere( qb.equalTo( attribute, values.get( 0 ) ) );
+        final List<? extends Comparable<?>> filterValues = values.stream().filter( Objects::nonNull ).toList();
+        if ( filterValues.size() > 1 ) {
+            qb.andWhere( qb.isIn( attribute, filterValues ) );
+        } else if ( filterValues.size() == 1 ) {
+            qb.andWhere( qb.equalTo( attribute, filterValues.get( 0 ) ) );
         }
     }
+
+    public boolean isEmpty() {
+        return values.isEmpty() || values.stream()
+                .allMatch( v -> Objects.isNull( v ) || (v instanceof final CharSequence cs && !StringUtils.hasText(
+                        cs )) );
+    }
 }

cursorpaging-jpa/src/main/java/io/vigier/cursorpaging/jpa/PageRequest.java

@@ -3,6 +3,8 @@
 import jakarta.persistence.Transient;
 import jakarta.persistence.metamodel.SingularAttribute;
 import java.util.ArrayList;
+import java.util.Collection;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.function.Consumer;
 import lombok.Builder;
@@ -44,8 +46,8 @@ public class PageRequest<E> {
     /**
      * The filters to apply to the query (removing results)
      */
-    @Singular
-    private final List<Filter> filters;
+    @Builder.Default
+    private final List<Filter> filters = new LinkedList<>();
 
     /**
      * The filter rules to apply to the query (removing results). Note that filter rules are <i>not</i> passed to the
@@ -120,6 +122,38 @@ public PageRequestBuilder<E> desc( final Attribute attribute ) {
             return addPosition( Position.create( b -> b.attribute( attribute ).order( Order.DESC ) ) );
         }
 
+        /**
+         * Add a filter to the request. Filter which do not contain a filter value or empty char-sequences as values are
+         * silently ignored for convenience reasons when creating page requests out of query parameters.
+         *
+         * @param filter A new filter definition
+         * @return the builder
+         */
+        public PageRequestBuilder<E> filter( final Filter filter ) {
+            if ( this.filters$value == null ) {
+                this.filters$value = new LinkedList<>();
+            }
+            if ( filter != null && !filter.isEmpty() ) {
+                this.filters$value.add( filter );
+                this.filters$set = true;
+            }
+            return this;
+        }
+
+        /**
+         * Add a list of filters to the page request. Filter which do not contain a filter value or empty char-sequences
+         * as values are silently ignored for convenience reasons when creating page requests out of query parameters.
+         *
+         * @param filters the list of filters to be added
+         * @return the builder
+         */
+        public PageRequestBuilder<E> filters( final Collection<Filter> filters ) {
+            if ( filters != null ) {
+                filters.forEach( this::filter );
+            }
+            return this;
+        }
+
         private PageRequestBuilder<E> addPosition( final Position pos ) {
             if ( this.positions == null ) {
                 this.positions = new ArrayList<>( 3 );

cursorpaging-jpa/src/test/java/io/vigier/cursorpaging/jpa/PageRequestTest.java

@@ -0,0 +1,33 @@
+package io.vigier.cursorpaging.jpa;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.NullAndEmptySource;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class PageRequestTest {
+
+    @ParameterizedTest
+    @NullAndEmptySource
+    @ValueSource( strings = { "  ", "\t", "\n" } )
+    void shouldIgnoreEmptyFilter( final String value ) {
+        final var pageRequest = PageRequest.create( b -> b.asc( Attribute.of( "id", Long.class ) )
+                .filter( Filter.create( f -> f.attribute( Attribute.of( "test", String.class ) ).value( value ) ) ) );
+
+        assertThat( pageRequest.filters() ).isEmpty();
+    }
+
+    @Test
+    void shouldAddPositionAndFilterIfValuePresent() {
+        final var pageRequest = PageRequest.create( b -> b.asc( Attribute.of( "id", Long.class ) )
+                .filter( Filter.create( f -> f.attribute( Attribute.of( "test", String.class ) ).value( "value" ) ) ) );
+
+        assertThat( pageRequest.filters() ).hasSize( 1 );
+        assertThat( pageRequest.positions() ).hasSize( 1 ).first().satisfies( p -> {
+            assertThat( p.attribute().name() ).isEqualTo( "id" );
+            assertThat( p.order() ).isEqualTo( Order.ASC );
+        } );
+    }
+}