DATAMONGO-784 - Polishing.

Add JavaDoc for compareValue.

Original pull request: #414.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperation.java

@@ -617,6 +617,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		/**
 		 * Generates a {@code $cmp} expression (compare to) that compares the value of the field to a given value or field.
 		 *
+		 * @param compareValue compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
@@ -627,6 +628,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		/**
 		 * Generates a {@code $eq} expression (equal) that compares the value of the field to a given value or field.
 		 *
+		 * @param compareValue compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
@@ -637,6 +639,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		/**
 		 * Generates a {@code $gt} expression (greater than) that compares the value of the field to a given value or field.
 		 *
+		 * @param compareValue compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
@@ -648,6 +651,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		 * Generates a {@code $gte} expression (greater than equal) that compares the value of the field to a given value or
 		 * field.
 		 *
+		 * @param compareValue compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
@@ -658,6 +662,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		/**
 		 * Generates a {@code $lt} expression (less than) that compares the value of the field to a given value or field.
 		 *
+		 * @param compareValue compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
@@ -669,6 +674,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		 * Generates a {@code $lte} expression (less than equal) that compares the value of the field to a given value or
 		 * field.
 		 *
+		 * @param compareValue the compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */
@@ -679,6 +685,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 		/**
 		 * Generates a {@code $ne} expression (not equal) that compares the value of the field to a given value or field.
 		 *
+		 * @param compareValue compare value or a {@link Field} object.
 		 * @return never {@literal null}.
 		 * @since 1.10
 		 */