Refactor null-checks.

Author: Gary Gregory

src/main/java/org/apache/commons/io/filefilter/PrefixFileFilter.java

@@ -133,9 +133,7 @@ public PrefixFileFilter(final String... prefixes) {
      * @since 1.4
      */
     public PrefixFileFilter(final String prefix, final IOCase ioCase) {
-        if (prefix == null) {
-            throw new IllegalArgumentException("The prefix must not be null");
-        }
+        requireNonNull(prefix, "prefix");
         this.prefixes = new String[] {prefix};
         this.isCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }
@@ -150,9 +148,7 @@ public PrefixFileFilter(final String prefix, final IOCase ioCase) {
      * @since 1.4
      */
     public PrefixFileFilter(final String[] prefixes, final IOCase ioCase) {
-        if (prefixes == null) {
-            throw new IllegalArgumentException("The array of prefixes must not be null");
-        }
+        requireNonNull(prefixes, "prefixes");
         this.prefixes = prefixes.clone();
         this.isCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }

src/main/java/org/apache/commons/io/filefilter/RegexFileFilter.java

@@ -117,9 +117,7 @@ public RegexFileFilter(final Pattern pattern) {
      * @since 2.10.0
      */
     public RegexFileFilter(final Pattern pattern, final Function<Path, String> pathToString) {
-        if (pattern == null) {
-            throw new IllegalArgumentException("Pattern is missing");
-        }
+        requireNonNull(pattern, "pattern");
         this.pattern = pattern;
         this.pathToString = pathToString;
     }

src/main/java/org/apache/commons/io/filefilter/SuffixFileFilter.java

@@ -135,9 +135,7 @@ public SuffixFileFilter(final String... suffixes) {
      * @since 1.4
      */
     public SuffixFileFilter(final String suffix, final IOCase ioCase) {
-        if (suffix == null) {
-            throw new IllegalArgumentException("The suffix must not be null");
-        }
+        requireNonNull(suffix, "suffix");
         this.suffixes = new String[] {suffix};
         this.ioCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }
@@ -152,9 +150,7 @@ public SuffixFileFilter(final String suffix, final IOCase ioCase) {
      * @since 1.4
      */
     public SuffixFileFilter(final String[] suffixes, final IOCase ioCase) {
-        if (suffixes == null) {
-            throw new IllegalArgumentException("The array of suffixes must not be null");
-        }
+        requireNonNull(suffixes, "suffixes");
         this.suffixes = suffixes.clone();
         this.ioCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }