Allow generate string of size 0

src/main/java/net/andreinc/mockneat/unit/text/Strings.java

@@ -36,7 +36,7 @@ public Strings(MockNeat mockNeat) {
     }
 
     public Strings size(int size) {
-        isTrue(size>0, SIZE_BIGGER_THAN_ZERO_STRICT);
+        isTrue(size>=0, SIZE_BIGGER_THAN_ZERO);
         this.size = size;
         return this;
     }

src/main/java/net/andreinc/mockneat/utils/ValidationUtils.java

@@ -35,7 +35,6 @@ public final class ValidationUtils {
     public static final String UPPER_BOUND_BIGGER_LOWER_BOUND = "The input parameter 'upperBound' > 'lowerBound'.";
     public static final String UPPER_MONTH_BIGGER_THAN_LOWER = "'lower' Month < 'upper' Month";
     public static final String IS_FINITE_NUMBER = "Number #{number} should be finite (non-infinite, non-nan).";
-    public static final String SIZE_BIGGER_THAN_ZERO_STRICT = "The size needs to be bigger than 0 (>).";
     public static final String SIZE_BIGGER_THAN_ZERO = "The size needs to be bigger than 0 (>=).";
     public static final String IN_RANGE_CLOSED = "Number: #{num} should be in [#{min}, #{max}] range.";
     public static final String CANNOT_ADD_VALUE_TO_COLLECTION = "Cannot add value '#{val}' to collection '#{cls.simpleName}'";

src/test/java/net/andreinc/mockneat/unit/text/StringsTest.java

@@ -22,6 +22,18 @@ public void testSizeNegative() {
         M.strings().size(-10).val();
     }
 
+    @Test
+    public void testSizeZero() {
+        loop(
+                1,
+                MOCKS,
+                (m) -> {
+                    String empty = m.strings().size(0).val();
+                    assertEquals(0, empty.length());
+                }
+        );
+    }
+
     @Test
     public void testVariableSizes() {
         loop(