imports:

import com.vividsolutions.jts.geom.*;
import gis.agne.counting.Value;
import org.geotools.data.FeatureSource;
import org.geotools.data.simple.SimpleFeatureCollection;
import org.geotools.data.simple.SimpleFeatureIterator;
import org.geotools.data.simple.SimpleFeatureSource;
import org.geotools.factory.CommonFactoryFinder;
import org.geotools.feature.DefaultFeatureCollection;
import org.geotools.feature.simple.SimpleFeatureBuilder;
import org.geotools.feature.simple.SimpleFeatureTypeBuilder;
import org.geotools.geometry.Envelope2D;
import org.geotools.geometry.GeometryBuilder;
import org.geotools.geometry.jts.GeometryClipper;
import org.geotools.geometry.jts.JTS;
import org.geotools.geometry.jts.JTSFactoryFinder;
import org.geotools.geometry.jts.ReferencedEnvelope;
import org.geotools.map.FeatureLayer;
import org.geotools.map.Layer;
import org.geotools.map.MapContent;
import org.geotools.referencing.crs.DefaultGeographicCRS;
import org.geotools.styling.*;
import org.geotools.swing.JMapFrame;
import org.geotools.swing.event.MapMouseEvent;
import org.opengis.feature.*;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;
import org.opengis.feature.type.AttributeDescriptor;
import org.opengis.feature.type.GeometryDescriptor;
import org.opengis.feature.type.Name;
import org.opengis.filter.Filter;
import org.opengis.filter.FilterFactory2;
import org.opengis.filter.identity.FeatureId;
import org.opengis.filter.sort.SortBy;
import org.opengis.geometry.BoundingBox;
import org.opengis.referencing.crs.CoordinateReferenceSystem;
import org.opengis.util.ProgressListener;

import javax.sound.sampled.Line;
import javax.swing.*;
import java.awt.*;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.geom.AffineTransform;
import java.awt.geom.Rectangle2D;
import java.io.IOException;
import java.text.DecimalFormat;
import java.util.*;
import java.util.List;

pom.xml:

    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>gis.agne</groupId>
  <artifactId>initial</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>initial</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <geotools.version>20-SNAPSHOT</geotools.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.geotools</groupId>
      <artifactId>gt-shapefile</artifactId>
      <version>${geotools.version}</version>
    </dependency>
    <dependency>
      <groupId>org.geotools</groupId>
      <artifactId>gt-epsg-hsql</artifactId>
      <version>${geotools.version}</version>
    </dependency>
    <dependency>
      <groupId>org.geotools.jdbc</groupId>
      <artifactId>gt-jdbc-postgis</artifactId>
      <version>${geotools.version}</version>
    </dependency>
    <dependency>
      <groupId>org.geotools</groupId>
      <artifactId>gt-swing</artifactId>
      <version>${geotools.version}</version>
    </dependency>
  </dependencies>
  <repositories>
    <repository>
      <id>maven2-repository.dev.java.net</id>
      <name>Java.net repository</name>
      <url>http://download.java.net/maven/2</url>
    </repository>
    <repository>
      <id>osgeo</id>
      <name>Open Source Geospatial Foundation Repository</name>
      <url>http://download.osgeo.org/webdav/geotools/</url>
    </repository>
    <repository>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
      <id>boundless</id>
      <name>Boundless Maven Repository</name>
      <url>http://repo.boundlessgeo.com/main</url>
    </repository>
  </repositories>
  <build>
    <plugins>
      <plugin>
        <inherited>true</inherited>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

I tried to build new type, but SimpleFeatureType.getCoordinateReferenceSystem() returns null

     Style style = SLD.createLineStyle(Color.BLUE, 1);
        Layer layer = new FeatureLayer(features, style);
        layer.setTitle("GARDEN");
        layerManager.addLayer(layer);
        return layer;
    }

    private DefaultFeatureCollection paintGarden (Coordinate[] coordinates, CoordinateReferenceSystem coordinateReferenceSystem) {
        //create polygon
        GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory( );
        com.vividsolutions.jts.geom.Polygon polygonFromCoordinates = geometryFactory.createPolygon(coordinates);

        SimpleFeatureTypeBuilder b = new SimpleFeatureTypeBuilder();

//set the name
        b.setName( "Garden" );

//add some properties
        b.add( "name", String.class );

//add a geometry property
        b.setCRS( coordinateReferenceSystem); // set crs first
        b.add( "location", Polygon.class ); // then add geometry
        b.crs(coordinateReferenceSystem);
//build the type
        final SimpleFeatureType FLAG = b.buildFeatureType();
        System.out.println(FLAG.getCoordinateReferenceSystem());
        SimpleFeatureBuilder builder = new SimpleFeatureBuilder(FLAG);
 
//add the values
        builder.add( "Sodas");
        builder.add(polygonFromCoordinates);

//build the feature with provided ID
        SimpleFeature feature = builder.buildFeature( "fid.1" );


        DefaultFeatureCollection featureCollection = new DefaultFeatureCollection("internal",FLAG);


        featureCollection.add( feature);

I tried to build new type, but SimpleFeatureType.getCoordinateReferenceSystem() returns null

     //create polygon
    GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory( );
    com.vividsolutions.jts.geom.Polygon polygonFromCoordinates = geometryFactory.createPolygon(coordinates);

    SimpleFeatureTypeBuilder b = new SimpleFeatureTypeBuilder();

    // set the name
    b.setName("Garden");

    // add some properties
    b.add("name", String.class);

    // add a geometry property
     CoordinateReferenceSystem coordinateReferenceSystem = DefaultGeographicCRS.WGS84;

    b.setCRS(coordinateReferenceSystem); // set crs first
    b.add("location", Polygon.class); // then add geometry
    b.crs(coordinateReferenceSystem);
    // build the type
    final SimpleFeatureType FLAG = b.buildFeatureType();
    System.out.println(FLAG.getCoordinateReferenceSystem());

    System.out.println(FLAG);