Adding a IsNullPredicate to handle absent values, especially when Equ…

…alPredicate is used

gbif/occurrence#244

src/main/java/org/gbif/api/model/occurrence/predicate/IsNullPredicate.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2020 Global Biodiversity Information Facility (GBIF)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.gbif.api.model.occurrence.predicate;
+
+import org.gbif.api.model.occurrence.search.OccurrenceSearchParameter;
+
+import java.util.Objects;
+import java.util.StringJoiner;
+
+import javax.validation.constraints.NotNull;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public class IsNullPredicate implements Predicate {
+
+  @NotNull
+  private final OccurrenceSearchParameter parameter;
+
+  @JsonCreator
+  public IsNullPredicate(@JsonProperty("parameter") OccurrenceSearchParameter parameter) {
+    Objects.requireNonNull(parameter, "<parameter> may not be null");
+    this.parameter = parameter;
+    checkPredicateAllowed();
+  }
+
+  public OccurrenceSearchParameter getParameter() {
+    return parameter;
+  }
+
+  /**
+   * @throws IllegalArgumentException if the key SearchParameter is Geometry
+   */
+  private void checkPredicateAllowed() {
+    if (OccurrenceSearchParameter.GEOMETRY == parameter) {
+      throw new IllegalArgumentException("IsNull predicate is not supported for Geometry parameter");
+    }
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    IsNullPredicate that = (IsNullPredicate) o;
+    return parameter == that.parameter;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(parameter);
+  }
+
+  @Override
+  public String toString() {
+    return new StringJoiner(", ", IsNullPredicate.class.getSimpleName() + "[", "]")
+      .add("parameter=" + parameter)
+      .toString();
+  }
+}