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The
NULL type
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isset() - Determine if a variable is set and is not NULL
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is_bool() - Finds out whether a variable is a boolean
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is_numeric() - Finds whether a variable is a number or a numeric string
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is_float() - Finds whether the type of a variable is float
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is_int() - Find whether the type of a variable is integer
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is_string() - Find whether the type of a variable is string
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is_object() - Finds whether a variable is an object
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is_array() - Finds whether a variable is an array
