Explain new PHP handling of non-numeric values by sum() and avg()

src/Map.php

@@ -525,6 +525,8 @@ public function at( int $pos )
  * The first line will return "3", the second and third one "2", the forth
  * one "30" and the last one "40".
  *
+ * NULL values are treated as 0, non-numeric values will generate an error.
+ *
  * This does also work for multi-dimensional arrays by passing the keys
  * of the arrays separated by the delimiter ("/" by default), e.g. "key1/key2/key3"
  * to get "val" from ['key1' => ['key2' => ['key3' => 'val']]]. The same applies to
@@ -4661,6 +4663,8 @@ public function suffix( $suffix, int $depth = null ) : self
  * The first line will return "9", the second one "6", the third one "90"
  * and the last one "80".
  *
+ * NULL values are treated as 0, non-numeric values will generate an error.
+ *
  * This does also work for multi-dimensional arrays by passing the keys
  * of the arrays separated by the delimiter ("/" by default), e.g. "key1/key2/key3"
  * to get "val" from ['key1' => ['key2' => ['key3' => 'val']]]. The same applies to

tests/MapTest.php

@@ -142,7 +142,7 @@ public function testAvg()
  {
  $this->assertSame( 3.0, Map::from( [1, 3, 5] )->avg() );
  $this->assertSame( 2.0, Map::from( [1, null, 5] )->avg() );
- $this->assertSame( 2.0, Map::from( [1, 'sum', 5] )->avg() );
+ $this->assertSame( 2.0, Map::from( [1, 0.0, 5] )->avg() );
  }
 
 
@@ -3070,7 +3070,7 @@ public function testSuffix()
  public function testSum()
  {
  $this->assertSame( 9.0, Map::from( [1, 3, 5] )->sum() );
- $this->assertSame( 6.0, Map::from( [1, 'sum', 5] )->sum() );
+ $this->assertSame( 6.0, Map::from( [1, 0.0, 5] )->sum() );
  }