Change to a proper exception

src/main/java/org/cactoos/Text.java

@@ -69,11 +69,15 @@ public NoNulls(final Text text) {
         @Override
         public String asString() throws IOException {
             if (this.origin == null) {
-                throw new IOException("NULL instead of a valid text");
+                throw new IllegalArgumentException(
+                    "NULL instead of a valid text"
+                );
             }
             final String string = this.origin.asString();
             if (string == null) {
-                throw new IOException("NULL instead of a valid result string");
+                throw new IllegalStateException(
+                    "NULL instead of a valid result string"
+                );
             }
             return string;
         }

src/test/java/org/cactoos/TextTest.java

@@ -37,13 +37,13 @@
  */
 public final class TextTest {
 
-    @Test(expected = IOException.class)
-    public void failForNullText() throws IOException {
+    @Test(expected = IllegalArgumentException.class)
+    public void failForNullArgument() throws IOException {
         new Text.NoNulls(null).asString();
     }
 
-    @Test(expected = IOException.class)
-    public void failForReturnNullString() throws IOException {
+    @Test(expected = IllegalStateException.class)
+    public void failForNullResult() throws IOException {
         new Text.NoNulls(
             new Text() {
                 @Override
@@ -59,7 +59,7 @@ public int compareTo(final Text text) {
     }
 
     @Test
-    public void checkForNullText() throws Exception {
+    public void okForNoNulls() throws Exception {
         final String message = "Hello";
         MatcherAssert.assertThat(
             "Can't work with null text",