Replace Stream usage with iteration to avoid non-null requirements.

SpelEvaluator now iterates over the parameter map instead of using the Java 8 Stream API. Previously, expressions resulting in a null value failed in the collector as Java 8 streams require non-null values for map values.

Closes #2904

src/main/java/org/springframework/data/repository/query/SpelEvaluator.java

@@ -15,9 +15,8 @@
  */
 package org.springframework.data.repository.query;
 
+import java.util.LinkedHashMap;
 import java.util.Map;
-import java.util.Map.Entry;
-import java.util.stream.Collectors;
 
 import org.springframework.data.repository.query.SpelQueryContext.SpelExtractor;
 import org.springframework.data.spel.ExpressionDependencies;
@@ -62,11 +61,12 @@ public Map<String, Object> evaluate(Object[] values) {
 
 		Assert.notNull(values, "Values must not be null.");
 
+		Map<String, String> parameterMap = extractor.getParameterMap();
+		Map<String, Object> results = new LinkedHashMap<>(parameterMap.size());
 
-		return extractor.getParameters().collect(Collectors.toMap(//
-				Entry::getKey, //
-				it -> getSpElValue(it.getValue(), values) //
-		));
+		parameterMap.forEach((parameter, expression) -> results.put(parameter, getSpElValue(expression, values)));
+
+		return results;
 	}
 
 	/**

src/main/java/org/springframework/data/repository/query/SpelQueryContext.java

@@ -22,11 +22,9 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.function.BiFunction;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
-import java.util.stream.Stream;
 
 import org.springframework.data.domain.Range;
 import org.springframework.data.domain.Range.Bound;
@@ -288,9 +286,6 @@ Map<String, String> getParameterMap() {
 			return expressions;
 		}
 
-		Stream<Entry<String, String>> getParameters() {
-			return expressions.entrySet().stream();
-		}
 	}
 
 	/**

src/test/java/org/springframework/data/repository/query/SpelEvaluatorUnitTests.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.springframework.data.repository.query;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.lang.reflect.Method;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.data.repository.query.SpelQueryContext.SpelExtractor;
+
+/**
+ * Unit tests for {@link SpelEvaluator}.
+ *
+ * @author Mark Paluch
+ */
+class SpelEvaluatorUnitTests {
+
+	final SpelQueryContext context = SpelQueryContext.of((counter, s) -> String.format("__$synthetic$__%d", counter + 1),
+			String::concat);
+
+	@Test // GH-2904
+	void shouldEvaluateExpression() throws Exception {
+
+		SpelExtractor extractor = context.parse("SELECT :#{#value}");
+		Method method = MyRepository.class.getDeclaredMethod("simpleExpression", String.class);
+		SpelEvaluator evaluator = new SpelEvaluator(QueryMethodEvaluationContextProvider.DEFAULT,
+				new DefaultParameters(method), extractor);
+
+		assertThat(evaluator.getQueryString()).isEqualTo("SELECT :__$synthetic$__1");
+		assertThat(evaluator.evaluate(new Object[] { "hello" })).containsEntry("__$synthetic$__1", "hello");
+	}
+
+	@Test // GH-2904
+	void shouldAllowNullValues() throws Exception {
+
+		SpelExtractor extractor = context.parse("SELECT :#{#value}");
+		Method method = MyRepository.class.getDeclaredMethod("simpleExpression", String.class);
+		SpelEvaluator evaluator = new SpelEvaluator(QueryMethodEvaluationContextProvider.DEFAULT,
+				new DefaultParameters(method), extractor);
+
+		assertThat(evaluator.getQueryString()).isEqualTo("SELECT :__$synthetic$__1");
+		assertThat(evaluator.evaluate(new Object[] { null })).containsEntry("__$synthetic$__1", null);
+	}
+
+	interface MyRepository {
+
+		void simpleExpression(String value);
+
+	}
+}