diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AbstractAggregationExpression.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AbstractAggregationExpression.java
index 573eed4a1..ec0a8ff8f 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AbstractAggregationExpression.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AbstractAggregationExpression.java
@@ -23,6 +23,7 @@ import java.util.List;
 import java.util.Map;
 
 import org.bson.Document;
+import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -101,9 +102,7 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 			List<Object> clone = new ArrayList<Object>((List) this.value);
 
 			if (value instanceof List) {
-				for (Object val : (List) value) {
-					clone.add(val);
-				}
+				clone.addAll((List) value);
 			} else {
 				clone.add(value);
 			}
@@ -116,9 +115,8 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 	@SuppressWarnings("unchecked")
 	protected java.util.Map<String, Object> append(String key, Object value) {
 
-		if (!(this.value instanceof java.util.Map)) {
-			throw new IllegalArgumentException("o_O");
-		}
+		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
+
 		java.util.Map<String, Object> clone = new LinkedHashMap<>((java.util.Map) this.value);
 		clone.put(key, value);
 		return clone;
@@ -144,6 +142,7 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 	 * @return
 	 * @since 2.1
 	 */
+	@SuppressWarnings("unchecked")
 	protected <T> T get(int index) {
 		return (T) values().get(index);
 	}
@@ -156,11 +155,10 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 	 * @return
 	 * @since 2.1
 	 */
+	@SuppressWarnings("unchecked")
 	protected <T> T get(Object key) {
 
-		if (!(this.value instanceof java.util.Map)) {
-			throw new IllegalArgumentException("o_O");
-		}
+		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
 
 		return (T) ((java.util.Map<String, Object>) this.value).get(key);
 	}
@@ -171,11 +169,10 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 	 * @since 2.1
 	 * @return
 	 */
+	@SuppressWarnings("unchecked")
 	protected java.util.Map<String, Object> argumentMap() {
 
-		if (!(this.value instanceof java.util.Map)) {
-			throw new IllegalArgumentException("o_O");
-		}
+		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
 
 		return Collections.unmodifiableMap((java.util.Map) value);
 	}
@@ -187,6 +184,7 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 	 * @return
 	 * @since 2.1
 	 */
+	@SuppressWarnings("unchecked")
 	protected boolean contains(Object key) {
 
 		if (!(this.value instanceof java.util.Map)) {
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java
index 640bd60fe..f64703b98 100755
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java
@@ -1078,6 +1078,29 @@ public class ProjectionOperationUnitTests {
 				"{ $project: { dayOfYear: { $dayOfYear: { \"date\" : \"$date\", \"timezone\" : \"America/Chicago\" } } } }"));
 	}
 
+	@Test // DATAMONGO-1834
+	public void shouldRenderTimeZoneFromField() {
+
+		Document agg = project()
+				.and(DateOperators.dateOf("date").withTimezone(Timezone.ofField("tz")).dayOfYear()).as("dayOfYear")
+				.toDocument(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(agg).isEqualTo(Document.parse(
+				"{ $project: { dayOfYear: { $dayOfYear: { \"date\" : \"$date\", \"timezone\" : \"$tz\" } } } }"));
+	}
+
+	@Test // DATAMONGO-1834
+	public void shouldRenderTimeZoneFromExpression() {
+
+		Document agg = project()
+				.and(DateOperators.dateOf("date")
+						.withTimezone(Timezone.ofExpression(LiteralOperators.valueOf("America/Chicago").asLiteral())).dayOfYear())
+				.as("dayOfYear").toDocument(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(agg).isEqualTo(Document.parse(
+				"{ $project: { dayOfYear: { $dayOfYear: { \"date\" : \"$date\", \"timezone\" : { $literal: \"America/Chicago\"} } } } }"));
+	}
+
 	@Test // DATAMONGO-1536
 	public void shouldRenderDayOfMonthAggregationExpression() {